Jiuzhi Plastics Network has collected the 25 most common problems related to mold manufacturing, mainly on cutting, and hopes to help the industry.
1. What is the most important and most decisive factor in choosing a mold steel?
A: Forming methodâ€”you can choose from two basic material types.
A) Hot-worked tool steel that withstands relatively high temperatures during die casting, forging and extrusion.
B) Cold-worked tool steel for blanking and shearing, cold forming, cold extrusion, cold forging and powder press forming.
Plastic - Some plastics produce corrosive by-products such as PVC plastic. Condensation, corrosive gases, acids, cooling/heating, water or storage conditions caused by prolonged shutdowns can also cause corrosion. In these cases, stainless steel is recommended.
Dimensions - Large sizes often use pre-hardened steel. Integral hardened steel is often used in small sizes.
Number of uses - Long-term use (> 1 000 000 times) should use high hardness steel with a hardness of 48-65 HRC. For medium long-term use (100 000 to 1 000 000), pre-hardened steel should be used with a hardness of 30-45 HRC. Short-term use (<100 000) to use mild steel, with a hardness of 160-250 HB.
Surface Roughness - Many plastic manufacturers are interested in good surface roughness. When sulfur is added to improve metal cutting performance, the surface quality is thus degraded. Steels with high sulfur content also become more brittle.
2. What are the primary factors that affect the machinability of materials?
A: The chemical composition of steel is very important. The higher the alloy composition of steel, the harder it is to process. As the carbon content increases, the metal cutting performance decreases.
The structure of the steel is also very important for metal cutting performance. Different structures include: forged, cast, extruded, rolled and machined. Forgings and castings have very difficult to machine surfaces.
Hardness is an important factor affecting the metal cutting performance. The general rule is that the harder the steel, the harder it is to process. High speed steel (HSS) can be used to machine materials up to 330-400 HB; high speed steel + titanium nitride (TiN) coatings can process materials up to 45 HRC; for materials with hardness 65-70 HRC Cemented carbide, ceramic, cermet and cubic boron nitride (CBN) must be used.
Non-metallic inclusions generally have an adverse effect on tool life. For example, Al2O3 (alumina), which is a pure ceramic, has a strong abrasiveness. The last one is residual stress, which can cause metal cutting performance problems. It is often recommended to perform a stress relief process after roughing.
3. What are the production costs of mold manufacturing?
A: Roughly speaking, the distribution of costs is as follows:
Cutting 65% workpiece material 20%
Heat treatment 5% assembly / adjustment 10%
This also clearly demonstrates the importance of good metal cutting performance and excellent overall cutting solutions for economic production.
4. What is the cutting characteristics of cast iron?
A: Generally speaking, it is: the higher the hardness and strength of cast iron, the lower the metal cutting performance, the lower the life expectancy from the blade and the tool. Most types of metal cast iron used in metal cutting production generally perform well. Metal cutting performance is related to structure, and harder pearlitic cast iron is more difficult to process. Flake graphite cast iron and malleable cast iron have excellent cutting properties, while ductile iron is quite poor.
The main types of wear encountered when machining cast iron are abrasion, bonding and diffusion wear. Abrasive is mainly produced by carbides, sand inclusions and hard cast skin. Bond wear with built-up edge occurs at low cutting temperatures and cutting speeds. The ferrite portion of cast iron is the easiest to weld to the insert, but this can be overcome by increasing the cutting speed and temperature.
On the other hand, diffusion wear is temperature dependent and occurs at high cutting speeds, especially when using high strength cast iron grades. These grades have high resistance to deformation and result in high temperatures. This wear is related to the interaction between the cast iron and the tool, which allows some cast irons to be machined at high speeds using ceramic or cubic boron nitride (CBN) tools for good tool life and surface quality.
Typical tool properties required for machining cast iron are: high heat hardness and chemical stability, but also related to process, workpiece and cutting conditions; the cutting edge is required to have toughness, heat fatigue wear and edge strength. The degree of satisfaction with cutting cast iron depends on how the wear of the cutting edge develops: rapid bluntness means hot cracks and gaps that cause premature cutting of the cutting edge, damage to the workpiece, poor surface quality, excessive waviness, and the like. Normal flank wear, balance and sharp cutting edges are just what you need to do.
5. What are the main and common processing steps in mold making?
A: Manufacturing must go through the cutting process, which should be divided into at least 3 process types:
Roughing, semi-finishing and finishing, and sometimes even super finishing (mostly high-speed cutting applications). The residual milling is of course prepared for finishing after the semi-finishing process. It is important to work hard in each process to leave a uniform distribution of allowance for the next process. If the direction of the tool path and the workload are rarely changed quickly, the tool life may be extended and more predictable. If possible, the finishing process should be performed on a dedicated machine. This will increase the geometric accuracy and quality during shorter commissioning and assembly times.
6. Which tool should be used primarily in these different processes?
Answer: Roughing process: round insert milling cutter, ball end mill and end mill with arc radius.
Semi-finishing operations: circular blade cutter (round blade cutters diameter range of 10-25 mm), a ball end mill.
Finishing process: round insert milling cutter, ball end mill.
Residual milling process: round insert milling cutter, ball end mill, vertical mill.
It is important to optimize the cutting process by selecting a specific combination of tool size, geometry and grade, as well as cutting parameters and appropriate milling strategies.
7. Is there one of the most important factors in the cutting process?
A: One of the most important goals in the cutting process is to create an evenly distributed machining allowance for each tool in each process. This means that tools of different diameters (from large to small) must be used, especially in roughing and semi-finishing operations. The primary criterion at all times should be as close as possible to the final shape in each process.
Providing a uniform distribution of machining allowance for each tool guarantees constant and high productivity and a safe cutting process. When ap/ae (axial cutting depth/radial cutting depth) is constant, the cutting speed and feed rate can also be constantly maintained at a high level. In this way, the mechanical action and the workload change on the cutting edge are small, so that less heat and fatigue are generated, thereby increasing the tool life. If the latter process is a semi-finishing process, especially for all finishing processes, unmanned or partially unprocessed. Constant material machining allowance is also the basic standard for high speed cutting applications.
Another advantageous effect of a constant machining allowance is the small adverse effect on the machine tool, the guide rails, the ball screw and the spindle bearings.
8. Why do you most often use round insert milling cutters as the first choice for mold roughing tools?
A: If the shoulder milling cutter is used for rough milling of the cavity, a large amount of stepped cutting allowance is removed in the semi-finishing process. This will cause the cutting force to change and the tool to bend. The result is an uneven machining allowance for the finishing, which affects the geometric accuracy. If a square shoulder cutter with a weaker tip (with a triangular blade) is used, an unpredictable cutting effect can result. Triangular or diamond-shaped inserts also produce greater radial cutting forces, and because of the small number of cutting edges, they are less economical roughing tools.
On the other hand, round inserts can be milled in a variety of materials and in all directions. If used, smooth transitions between adjacent passes can also result in smaller and more uniform processing for semi-finishing. One of the characteristics of the round inserts is that the chip thickness they produce is variable. This allows them to use a higher feed rate than most other blades. The main blade of the circular blade changes from almost zero (very shallow cutting) to 90 degrees, and the cutting action is very smooth. At the maximum depth of the cut, the lead angle is 45 degrees, and when cutting along a straight wall with an outer circle, the lead angle is 90 degrees. This also explains why the strength of the circular insert tool is large - the cutting load is gradually increasing. Roughing and semi-roughing should always be the first choice for round insert milling cutters such as CoroMill 200 (see manufacturing sample C-1102:1). In 5-axis cutting, the round insert is very suitable, especially without any restrictions.
By using good programming, round insert milling cutters can largely replace ball end mills. The combination of a circular blade with a small amount of runout, combined with a finely ground, positive rake and light cutting geometry, can also be used for semi-finishing and some finishing operations.
9. What is the effective cutting speed (ve) and why is it important for high productivity?
A: The basic calculation of the effective cutting speed on the actual or effective diameter during cutting is always very important. Since the table feed depends on the speed at a certain cutting speed, if the effective speed is not calculated, the table feed will be calculated incorrectly.
If the tool's nominal diameter value (Dc) is used in calculating the cutting speed, the effective or actual cutting speed is much lower than the calculated speed when the cutting depth is shallow. The circular blade cutter CoroMill 200 (especially in the small diameter range), ball mill, a large nose radius end mill and a milling cutter tool CoroMill 390 or the like (see the knives Sandvik Coromant Make sample C-1102: 1). As a result, the calculated feed rate is also much lower, which severely reduces productivity. More importantly, the cutting conditions of the tool are lower than its capabilities and recommended application range.
When 3D cutting is performed, the diameter at the time of cutting changes, which is related to the geometry. One solution to this problem is to define a steep wall area and a shallow geometrical part area. Good compromises and results can be achieved if specialized CAM procedures and cutting parameters are programmed for each zone.
10. What are the important application parameters for successful hardened die steel milling?
A: When finishing high-speed milling of hardened steel, one of the main factors to be observed is shallow cutting. The depth of cut should not exceed 0.2/0.2 mm (ap/ae: axial depth of cut / radial depth of cut). This is to avoid excessive bending of the tool holder/cutting tool and to maintain a small tolerance and high precision.
It is also important to choose a very rigid clamping system and tool. When using solid carbide tools, it is important to use tools with the largest core diameter (maximum flexural rigidity). A rule of thumb is that if the diameter of the tool is increased by 20%, for example from 10 mm to 12 mm, the bending of the tool will be reduced by 50%. It can also be said that if the tool overhang/extension is shortened by 20%, the bending of the tool will be reduced by 50%. Large diameter and tapered shanks further increase stiffness. When using ball end mills with indexable inserts (see manufacturing sample C-1102:1), if the shank is made of solid carbide, the bending rigidity can be increased by 3-4 times.
When finishing hardened steel with high speed milling, it is also important to choose a special geometry and grade. It is also important to choose a coating with a high heat hardness like TiAlN.
11. When should I use down-cutting and when should I use up-cut milling?
A: The main recommendations are: Use as much milling as possible.
When the cutting edge is just cutting, the chip thickness can reach its maximum value in the down-cut milling. In the case of up-cut milling, it is the minimum value. In general, tool life in up-cut milling is shorter than in down-cut milling because the heat generated in up-cut milling is significantly higher than in down-cut milling. When the chip thickness is increased from zero to maximum in up-cut milling, more heat is generated because the cutting edge is subjected to a higher friction than in the down-milling. The radial force is also significantly higher in up-cut milling, which has an adverse effect on the spindle bearings.
In down-cut milling, the cutting edge is mainly subjected to compressive stress, which is much more advantageous for cemented carbide inserts or solid carbide tools than for the tensile forces generated in up-cut milling. of course there are exceptions. When using a solid carbide end mill (see tool in C- 1102:1) for side milling (finishing), especially in hardened materials, up-cut milling is preferred. This makes it easier to obtain wall straightness with a smaller tolerance and a better 90 degree angle. If there is a misalignment between the different axial passes, the tool marks are also very small. This is mainly due to the direction of the cutting force. If a very sharp cutting edge is used in the cutting, the cutting force tends to "pull" the knife toward the material. Another example of the use of up-cut milling is the use of old-fashioned manual milling machines for milling, where the screw of the old-fashioned milling machine has a large gap. Up-cut milling produces a cutting force that eliminates the gap, making the milling movement smoother.
12. Copy milling or contour cutting?
A: In pocket milling, the best way to ensure a successful path to a milling tool is to use a contour milling path. Milling knives (eg ball end mills, see manufacturing sample C-1102:1) Milling of the outer circle along the contour often results in high productivity because more teeth are being cut at larger tool diameters. If the spindle speed of the machine is limited, contour milling will help maintain cutting speed and feed rate. With this tool path, the change in workload and direction is also small. This is especially important in high speed milling applications and in hardened material processing. This is because if the cutting speed and feed rate are high, the cutting edge and the cutting process are more susceptible to the adverse effects of changes in the workload and direction. Changes in the work load and direction can cause changes in the cutting force and tool bending. Profiling along the steep wall should be avoided as much as possible. When copy milling, the chip thickness at low cutting speed is large. In the center of the ball-end knife, there is a danger of the blade being broken. If the control is poor, or the machine has no read-ahead function, it cannot be decelerated quickly enough, and the risk of chipping at the center is most likely to occur. The upper profile milling along the steep wall is better for the cutting process because the chip thickness is at its maximum at favorable chip speeds.
In order to achieve the longest tool life, the cutting edge should be kept in continuous cutting for as long as possible during the milling process. If the tool enters and exits too frequently, the tool life will be significantly shortened. This will exacerbate thermal stress and thermal fatigue on the cutting edge. It is more advantageous for modern carbide tools to have uniform and high temperatures in the cutting area than to have large fluctuations. The profiling milling path is often a mixture of up-cut and down-cut (zigzag), which means that the knife is frequently eaten and retracted during cutting. This tool path also has a bad influence on quality. Each time a knife is used, it means that the tool is bent and there is a mark on the surface. When the tool exits, the cutting force and the bending of the tool are reduced, and there is a slight material "overcutting" in the exit portion.
13. Why do some milling cutters have different pitches?
A: The milling cutter is a multi-edge cutting tool. The number of teeth (z) can be changed. There are some factors that can help determine the pitch or number of teeth for different machining types. Materials, workpiece dimensions, overall stability, overhang dimensions, surface quality requirements, and available power are processing-related factors. Tool-related factors include enough feed per tooth, at least two teeth at the same time, and the chip capacity of the tool, which are only a small part of it.
The pitch (u) of the milling cutter is the distance from the point on the cutting edge of the insert to the same point on the next cutting edge. Milling cutters are divided into sparse, dense and ultra-thick pitch milling cutters. Most of the Coromant milling cutters have these three options. See manufacturing sample C-1102:1. The dense pitch means that there are more teeth and proper chip space, which can be cut with high metal removal rate. Generally used for medium load milling of cast iron and steel. The fine pitch is the first choice for general purpose milling cutters and is recommended for mixed production.
The sparse pitch means that there are fewer teeth and a large chip space on the circumference of the milling cutter. Spacing is often used for roughing to finishing of steel. Vibration in steel processing has a great influence on the processing results. Spalling is a truly effective solution to problems. It is the first choice for long overhang milling, low power machines or other applications where cutting forces must be reduced.
The ultra-precision tool has a very small chip space and can be fed with a higher table. These tools are suitable for cutting of interrupted cast iron surfaces, cast iron roughing and small residual machining of steel, such as side milling. They are also suitable for applications where low cutting speeds must be maintained. Milling cutters can also have uniform or unequal pitches. The latter refers to the unequal spacing of the teeth on the tool, which is also an effective way to solve the vibration problem.
When there is a vibration problem, it is recommended to use a toothless unequal pitch milling cutter as much as possible. Since there are fewer blades, the possibility of increased vibration is small. Small tool diameters can also improve this situation. A combination of well-adapted troughs and grades should be used â€“ a combination of sharp cutting edges and toughness.
14. How should the milling cutter be positioned for optimum performance?
A: The cutting length is affected by the position of the milling cutter. Tool life is often related to the length of cutting that the cutting edge must bear. The milling cutter positioned in the center of the workpiece has a short cutting length. If the milling cutter is offset from the center line in either direction, the cutting arc is long. Keep in mind how the cutting force works and must achieve a compromise. With the tool positioned in the center of the workpiece, the direction of the radial cutting force changes as the cutting edge of the blade enters or exits the cutting. The gap in the machine tool spindle also exacerbates the vibration, causing the blade to vibrate.
By deviating the tool from the center, a constant and favorable cutting force direction is obtained. The longer the overhang, the more important it is to overcome all possible vibrations.
15. What measures should be taken to eliminate vibration during cutting?
A: When there is a vibration problem, the basic measure is to reduce the cutting force. This can be achieved by using the correct tool, method and cutting parameters.
Follow the proven recommendations below:
- Select a sparse or unequal pitch cutter.
- Use positive rake angle, small cutting force blade geometry.
- Use a small milling cutter whenever possible. This is especially important when milling with a damper post.
- Blades with a small cutting edge passivation radius (ER). From thick coatings to thin coatings. Uncoated blades can be used if desired. High toughness insert grades with fine grained particles should be used.
- Use a large feed per tooth. Reduce the speed and keep the table feed (equal to a larger feed per tooth). Or maintain the speed and increase the table feed (larger feed per tooth). Never reduce the feed per tooth!
- Reduce radial and axial depth of cut.
- Choose a stable holder such as Coromant Capto. Use the largest possible adapter size for optimum stability. Use a taper extension to achieve maximum rigidity.
- For large overhangs, use a damper post that is combined with a pitch-toothed unequal pitch cutter. When installing the milling cutter, connect the milling cutter directly to the shock absorbing handle.
- Deviate the milling cutter from the center of the workpiece.
- If you use a tool with even teeth - you can remove one blade every other tooth.
16. What are the most important measures to be taken to balance the tool?
A: The typical steps involved in achieving tool balance throughout the cutting process are as follows:
- Measure the imbalance of the tool/toolholder assembly.
- Reduce the imbalance by changing the tool, cutting it to remove some mass, or moving the weight on the handle.
- These steps must often be repeated, including checking the tool again and fine-tuning again until equilibrium is reached.
Tool balancing also involves instability in several undiscussed processes. One of them is the problem of the fit between the shank and the spindle. The reason for this is that there is often a measurable gap during clamping, or there may be chips or dirt on the taper shank. This will cause the taper shank to be positioned differently each time. Even if the tool, the shank and the spindle are in good condition in all respects, if there is contamination, it will cause an imbalance. In order to balance the tool, the cost of the cutting process must be increased. If tool balancing is important to reduce costs, then each case should be analyzed.
However, in order to balance the tool well, there is still a lot of work to do when choosing the right tool. The following points should be considered when selecting a tool:
- Purchase high quality tools and holders. You should choose a tool holder that has been previously unbalanced.
- Purchase high quality tools and holders. You should choose a tool holder that has been previously unbalanced.
- It is best to use short and lightest tools.
- Regularly inspect the tool and the tool holder for signs of fatigue threads and deformation.
The tool imbalance that the process can accept is determined by the process itself. These conditions include the cutting force during the cutting process, the balance of the machine tool, and the extent to which these two factors interact with each other. Testing is the best way to find the best balance. Run several times with different imbalance values, for example starting with an imbalance value of 20 grams or less. Repeat the test with a more balanced tool after each run. The optimum balance should be such a point that after this point, further improvement of the tool balance does not increase the surface quality of the workpiece; or a point at which the process can easily guarantee the specified workpiece tolerance.
The key is to always focus on the process, rather than targeting the balance-G value or any other deterministic balance. This goal should be to achieve the highest possible efficiency of the process. This involves weighing the cost of tool balancing and the benefits that result from it, so a reasonable balance should be made between cost and benefit.
17. Which tool holder should I use in order to get the best possible results in conventional and high speed cutting applications?
A: When machining at high speed, the centrifugal force is very large, which will cause the spindle hole to gradually become larger. This has a negative effect on the shank of some V-flanges because the shank of the V-shaped flange only contacts the spindle bore on the radial face. The spindle hole change assembly causes the tool to be pulled into the spindle under the constant pulling force of the pull rod. This may even cause the tool to stick or the dimensional accuracy in the Z-axis direction to decrease.
The tool that is in simultaneous contact with the spindle hole and the end face, that is, the tool that is simultaneously matched in the radial direction and the axial direction, is more suitable for cutting at a high speed. When the spindle hole is enlarged, the end face contact prevents the tool from moving upward in the spindle hole. Tools using hollow shanks are also susceptible to centrifugal forces, but they have been designed to increase with increasing spindle bore at high speeds. The tool and the spindle are in radial and axial contact to provide good clamping rigidity, allowing the tool to be cut at high speeds. The Coromant Capto interface with its unique elliptical triangular short cone design delivers superior performance in torque and high productivity cutting.
Comparison table of spindle surface contact at high spindle speed
Spindle speed ISO 40 HSK 50A Coromant Capto C5
0 100% 100% 100%
20 000 100% 95% 100%
25 000 37% 91% 99%
30 000 31% 83% 95%
35 000 26% 72% 91%
40 000 26% 67% 84%
When arranging high-speed cutting, try to use a tool system that combines symmetrical tools and tool holders. There are several different tooling systems available. The shank is first heated to expand the holes, and the tool is clamped after they are cooled. This is the interference fit system. This is the best and most reliable method of fixed tooling for high speed cutting. This is first because its runout is very small; second, this connection can deliver high torque; third, it is easy to build custom tools and tool assemblies; finally, the tool assembly made up of this method has a very high overall rigidity.
Another outstanding and very versatile tool clamping device is CoroGrip, a Coromant high-precision power chuck. This tool holder system covers everything from roughing to super finishing. A collet can clamp all types of tools from the face milling cutter with straight shank, Wyeth or side pressure shank to the drill bit. Standard spring jackets, such as hydraulic grips (HydroGrip), BIG, Nikken, NT spring jackets, can be used with CoroGrip chucks. The runout at 4XD is only 0.002 â€“ 0.006 mm. The clamping force and torque transmission are particularly high, and its balanced design makes it ideal for high-speed cutting (< 40 000 rpm).
18. How should I cut the corners so that there is no risk of vibration?
A: The traditional method of cutting the corner is to use linear cutting (G1), the transition in the corner is not continuous. This means that when the tool reaches the corner, the tool must decelerate due to the dynamic characteristics of the linear axis. There is a brief pause before the motor changes the feed direction, which generates a lot of heat and friction. Very long contact lengths can result in unstable cutting forces and often result in insufficient corner cutting. The typical result is vibrationâ€”the larger and longer the tool, or the larger the total overhang of the tool, the stronger the vibration.
The best solution to this problem:
Use a tool with a smaller fillet radius than the corner radius. Use circular interpolation to create corners. This method of machining does not create a pause at the boundary of the block, which means that the movement of the tool provides a smooth and continuous transition, and the possibility of vibration is greatly reduced.
Another solution is to create a fillet radius that is slightly larger than the one specified on the drawing by circular interpolation. This is advantageous so that sometimes larger tools can be used in roughing to maintain high productivity.
The remaining machining allowance at the corner can be fixed milling or circular interpolation with a smaller tool.
19. What is the best way to start cutting the cavity?
A: There are 4 main methods:
Pre-drilling of the starting hole and pre-drilling of the corners. This method is not recommended: This requires the addition of a tool, which also occupies the tool room. From the point of view of cutting alone, the tool generates unfavorable vibration due to the cutting force when pre-drilling the hole. Tool damage is often caused when using pre-drilled holes. The use of pre-drilled holes also increases the re-cutting of the chips.
If a ball end mill or a round insert tool is used (see manufacturing sample C-1102:1), boring is usually used to ensure that all axial depths can be cut. Disadvantages of using this method are chip removal problems and the use of round inserts produces very long chips.
One of the best methods is to use linear slope cutting in the X/Y and Z directions to achieve full axial depth cutting. Finally, circular interpolation milling can be performed in a spiral form. This is a very good method because it produces a smooth cutting effect and requires only a small starting space.
20. What is the definition of high speed cutting?
A: The discussion of high-speed cutting is still somewhat confusing. There are many ideas and many ways to define high speed cutting (HSM). Let's take a look at a few of these definitions:
High cutting speed cutting
High spindle speed cutting
High feed cutting
High speed and high feed cutting
High productivity cutting
Our definition of high speed cutting is described as follows:
HSM is not a high cutting speed in the simple sense. It should be considered a process that is processed using specific methods and production equipment.
High-speed cutting does not require high-speed spindle cutting. Many high-speed cutting applications are based on medium-speed spindles and large-size tools.
If the hardened steel is finished at high cutting speeds and high feed conditions, the cutting parameters can be 4 to 6 times conventional. In the roughing of semi-finished parts to semi-finishing, finishing and ultra-finishing of any size part, HSM means high productivity cutting. As part shapes become more complex, high-speed cutting becomes more and more important. High-speed cutting is now mainly used on machine tools with a taper of 40.
21. What is the goal of high speed cutting?
A: One of the main goals of high-speed cutting is to reduce production costs through high productivity. It is mainly used in finishing processes and is often used to process hardened steel. Another goal is to increase overall competitiveness by reducing production time and delivery time.
The main factors to achieve these goals are:
One (less than this) clamping process.
Improved geometric accuracy through cutting while reducing manual labor and shortening test time.
Use CAM systems and shop-oriented programming to help develop process plans and improve machine and plant utilization through process planning.
22. What are the practical advantages of high speed cutting?
A: Tools and workpieces can be kept at low temperatures, which in many cases extends the life of the tool. On the other hand, in high-speed cutting applications, the amount of cutting is shallow, and the cutting edge of the cutting edge is extremely short. That is to say, the feed is faster than the heat.
Low cutting forces result in small, consistent tool bending. This, combined with the constant machining allowance required for each tool and process, is one of the prerequisites for efficient and safe machining.
Since the typical depth of cut in high speed cutting is shallow, the radial forces on the tool and spindle are low. This reduces wear on the spindle bearings, rails and ball screws. High-speed cutting and axial milling are also good combinations. They have a small impact on the spindle bearings. With this method, the tool with a long overhang can be used with little risk of vibration. High-productivity cutting of small-sized parts, such as roughing, semi-finishing, and finishing, is economical when the overall material removal rate is relatively low.
High-speed cutting achieves high productivity in general finishing and excellent surface quality. The surface quality is often lower than Ra 0.2 um. High-speed cutting makes it possible to cut thin-walled parts. With high-speed cutting, the knife time is short, and the impact and bending are reduced. The geometric accuracy is improved and assembly is easier and faster. The surface texture and geometric accuracy of CAM/CNC production can be obtained regardless of the person or skill. If the time spent on cutting is slightly more, the time-consuming manual polishing work can be significantly reduced. It can often be reduced by 60-100%. Some machining, such as quenching, electrolytic machining and electrical discharge machining (EDM), can be greatly reduced. This reduces investment costs and simplifies logistics. With cutting instead of electric discharge machining (EDM), the service life and quality are also improved. With high-speed cutting, the design can be changed quickly with CAD/CAM, especially without the need to produce new electrodes.
23. Is there a risk or a disadvantage to high speed cutting?
A: Due to the high acceleration and deceleration of the starting process and the stop, the guide rails, ball screws and spindle bearings produce relatively fast wear. This often leads to higher maintenance costs.
Requires specialized process knowledge, programming equipment, and an interface to quickly transfer data.
It may be difficult to find and select senior technical staff.
There is often a considerable amount of debugging and failure time.
There is no need for an emergency stop during processing, resulting in human error and software or hardware failures with many serious consequences.
There must be a good processing plan - "Providing food to hungry machine tools."
Safety measures must be taken: use a machine with a safety cover and a debris-proof cover. Avoid large overhangs of the tool. Do not use "heavy" tools and posts. Regularly check the tools, posts and bolts for fatigue cracks. Use only tools that indicate the highest spindle speed. Do not use integral high speed steel (HSS) tools!
24. What are the requirements for high speed cutting on machine tools?
A: The typical requirements for ISO/BT 40 machines are as follows:
Spindle speed range < 40 000 rpm
Spindle power > 22 kW
Programmable feed rate 40-60 m/min
Fast lateral feed < 90 m/min
Axial deceleration / acceleration of> 1 G
Block processing speed 1-20 ms
Data transfer speed 250 Kbit/s (1 ms)
Incremental (linear) 5-20 microns
Or NURBS interpolation
The spindle has high thermal stability and rigidity, and the spindle bearings have high pre-tension and cooling capacity.
Air supply/coolant through the main shaft
Rigid machine tool frame with high vibration absorption capacity
Various error compensations - temperature, quadrant, and ball screw are the most important.
Advanced predictive features in the CNC.
25. What are the typical characteristics or requirements of high-speed cutting for cutting tools?
A: Solid carbide:
High precision grinding with radial runout below 3 microns.
The smallest possible protrusion and overhang, the maximum rigidity, the bending deformation of the tool as small as possible and the large core diameter.
In order to minimize the risk of vibration, cutting forces and bending, the cutting edge and contact length should be as short as possible.
Oversized, tapered shank, which is especially important at small diameters.
Fine grain matrix and TiAlN coating for high wear resistance.
Internal cooling holes for air or coolant.
Robust micro-groove for high-speed cutting of hardened steel.
Symmetrical tools are best designed to ensure balance.
Tools using indexable inserts:
Designed to ensure a balance.
The high precision of the bobs on the insert holder and the blade is small, and the maximum radial runout of the main insert is 10 microns.
Grades and geometries for high speed cutting of hardened steel.
The knife has a proper clearance to avoid friction when the tool bending (cutting force) disappears.
Cooling holes for air or coolant (end mill).
The knife is specifically marked with the maximum allowable speed.
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