25 FAQs in the hottest mold manufacturing field 1

2022-08-26
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25 FAQs in the field of mold manufacturing (1)

1) what is the most important and decisive factor in selecting mold steel

forming method? You can choose from two basic material types

a) hot working tool steel, which can withstand relatively high temperature during mold casting, forging and extrusion

b) cold working tool steel, which is used for blanking and shearing, cold forming, cold extrusion, cold forging and powder pressure forming

plastics - "there is something fishy about the external wall insulation: inferior boards are flammable and bury huge fires." some plastics will produce corrosive by-products, such as PVC plastics. Factors such as condensation, corrosive gas, acid, cooling/heating, water or storage conditions caused by long-term shutdown will also cause corrosion. In these cases, die steel made of stainless steel is recommended

die size - pre hardened steel is often used for large-size dies. Integrally hardened steel is often used for small-size molds

mold use times - the mold used for a long time (1000000 times) should use high hardness steel with a hardness of 48-65 HRC. The mold used for medium and long time (100000 to 1000000 times) should use pre hardened steel with a hardness of 30-45 HRC. Short time use (surface roughness - many plastic mold manufacturers are interested in good surface roughness. When sulfur is added to improve metal cutting performance, the surface quality will be reduced. Steel with high sulfur content will also become more brittle.

2) what is the primary factor affecting the machinability of materials

the chemical composition of steel is very important. The higher the alloy composition of steel, the more difficult it is to machine. When the carbon content increases, the metal cutting performance decreases

the structure of steel is also very important for metal cutting performance. Different structures include: forged, cast, extruded, rolled and machined. Forgings and castings have surfaces that are very difficult to machine

hardness is an important factor affecting metal cutting performance. The general rule is that the harder the steel is, the harder it is to machine. High speed steel (HSS) can be used to process materials with the highest hardness of HB; High speed steel + titanium nitride (TIN) coating, which can process materials with a maximum hardness of 45 HRC; For materials with HRC hardness, cemented carbide, ceramics, cermets and cubic boron nitride (CBN) must be used

nonmetallic impurities generally have a negative impact on tool life. For example, Al2O3 (alumina), which is a pure ceramic, has strong abrasiveness

the last one is residual stress, which can cause problems in metal cutting performance. It is often recommended to carry out the stress relief process after rough machining

3) what is the production cost of mold manufacturing

roughly speaking, the distribution of cost is as follows:

cutting 65%

workpiece material 20%

heat treatment 5%

assembly/adjustment 10%

this also clearly shows the importance of good metal cutting performance and excellent overall cutting solutions to the economic production of molds

4) what are the cutting characteristics of cast iron

generally speaking, it is:

the higher the hardness and strength of cast iron, the lower the metal cutting performance, and the lower the expected life of blades and cutters. Cast iron used for metal cutting production generally has good metal cutting performance of most types. The metal cutting performance is related to the structure, and the processing of hard pearlitic cast iron is also difficult. Flake graphite cast iron and malleable cast iron have excellent cutting properties, while nodular cast iron is quite poor

the main types of wear encountered in processing cast iron are abrasion, bonding and diffusion wear. Abrasion is mainly caused by carbides, sand particles, impurities and hard cast skin. The adhesive wear with chip buildup occurs at low cutting temperature and cutting speed. The ferrite part of cast iron is the easiest to weld to the blade, but this can be overcome by increasing the cutting speed and temperature

on the other hand, diffusion wear is related to temperature and occurs at high cutting speeds, especially when high-strength cast iron grades are used. These brands have high resistance to deformation, resulting in high temperature. This kind of wear is related to the role between cast iron and tools, which makes some cast iron need ceramics or cubic nitrogen. Maybe we can make some adjustments to some materials that constitute the internal structure of the aircraft. Boron carbide (CBN) tools are processed at high speed to obtain good tool life and surface quality

generally, the typical tool attributes required for machining cast iron are: high thermal hardness and chemical stability, but also related to process, workpiece and cutting conditions; The cutting edge is required to have toughness, heat-resistant fatigue wear and edge strength. The degree of satisfaction of cutting cast iron depends on how the wear of the cutting edge develops: rapid blunting means the generation of thermal cracks and notches, resulting in premature fracture of the cutting edge, workpiece damage, poor surface quality, excessive waviness, etc. Normal flank wear, balance and sharp cutting edge are just what we generally need to do

5) what are the main and common processing procedures in mold manufacturing

the cutting process should be divided into at least three process types:

rough machining, semi finishing and finishing, and sometimes even super finishing (mostly high-speed cutting applications). Residual milling is, of course, prepared for finishing after the semi finishing process. In each process, we should strive to leave evenly distributed margin for the next process, which is very important. If the direction of the tool path and the workload rarely change rapidly, the tool life may be extended and more predictable. If possible, the finishing process should be carried out on a special machine tool. This will improve the geometric accuracy and quality of the mold in a shorter adjustment time, and many customers will always be careless in the trial and assembly time

6) what kind of tools should be used in these different processes

rough machining process: round blade milling cutter, ball end milling cutter and end milling cutter with large tip arc radius

semi finishing process: round blade milling cutter (round blade milling cutter with diameter range of 10-25 mm), ball end milling cutter

finishing process: round blade milling cutter, ball end milling cutter

residual milling process: round blade milling cutter, ball end milling cutter, vertical milling cutter

it is very important to optimize the cutting process by selecting special tool size, groove shape and brand combination, as well as cutting parameters and appropriate milling strategy

7) is there a most important factor in the cutting process

one of the most important goals in the cutting process is to create a uniformly distributed machining allowance for each tool in each process. That is to say, tools with different diameters (from large to small) must be used, especially in rough machining and semi finishing processes. At any time, the main standard should be as close as possible to the final shape of the mold in each process

provide evenly distributed machining allowance for each tool, ensuring constant and high productivity and safe cutting process. When ap/ae (axial cutting depth/radial cutting depth) is constant, the cutting speed and feed rate can also be kept at a high level. In this way, the mechanical action and working load change on the cutting edge are small, so the heat and fatigue generated are less, thus improving the tool life. If the following processes are semi finishing processes, especially all finishing processes, unmanned processing or partial unmanned processing can be carried out. Constant material machining allowance is also the basic standard for high-speed cutting applications

Another beneficial effect of constant machining allowance is that it has little adverse effect on machine tool guide rails, ball screws and spindle bearings

8) why is the round blade milling cutter most often used as the first choice for die rough machining

if the square shoulder milling cutter is used for rough milling of the cavity, a large amount of step shaped cutting allowance must be removed in semi finishing. This will change the cutting force and bend the tool. The result is to leave uneven machining allowance for finishing, which affects the geometric accuracy of the die. If square shoulder milling cutters (with triangular inserts) with weak tip strength are used, unpredictable cutting effects will occur. Triangular or rhombic inserts also produce greater radial cutting force, and because the number of cutting edges of the inserts is small, they are less economical rough machining tools

on the other hand, the round blade can be milled in various materials and in all directions. If it is used, the transition between adjacent tool paths is smoother, and smaller and more uniform machining allowance can also be left for semi finishing. One of the characteristics of round blades is that the chip thickness they produce is variable. This allows them to use a higher feed rate than most other blades. The main deflection angle of the round blade changes from almost zero (very shallow cutting) to 90 degrees, and the cutting effect is very stable. At the maximum depth of cutting, the main deflection angle is 45 degrees. When cutting along the straight wall with an outer circle, the main deflection angle is 90 degrees. This also explains why the strength of the round blade tool is high, and the cutting load increases gradually. Rough machining and semi rough machining should always use round blade milling cutters, such as coromill 200 (see mold manufacturing sample c-1102:1) as the first choice. In 5-axis cutting, the round blade is very suitable, especially it has no restrictions

by using good programming, the round blade milling cutter can replace the ball end milling cutter to a great extent. The circular blade with small runout, combined with fine grinding, positive rake angle and light cutting groove shape, can also be used in semi finishing and some finishing processes

9) what is the effective cutting speed (VE) and why is it important for high productivity

In

cutting, the basic calculation of the effective cutting speed on the actual or effective diameter is always very important. Since the table feed depends on the rotation speed at a certain cutting speed, if the effective speed is not calculated, the table feed will be calculated incorrectly

if the nominal diameter value (DC) of the tool is used when calculating the cutting speed, when the cutting depth is shallow, the effective or actual cutting speed is much lower than the calculated speed. Tools such as round blade coromill 200 tools (especially in the small diameter range), ball end mills, large tip arc radius end mills, and coromill 390 end mills (for these tools, see Sandvik's mold manufacturing sample c-1102:1). Thus, the calculated feed rate is also much lower, which seriously reduces the productivity. More importantly, the cutting condition of the tool is lower than its ability and recommended application range

when 3D cutting is carried out, the diameter during cutting is changing, which is related to the geometry of the die. One solution to this problem is to define the steep wall area of the mold and the part area with shallow geometry. If special cam programs and cutting parameters are programmed for each area, a good compromise and result can be achieved

10) what are the important application parameters for the successful milling of hardened die steel

when using high-speed milling to finish machining hardened die steel, a major factor to be observed is the use of shallow cutting. The cutting depth shall not exceed 0.2/0.2 mm (ap/ae: axial cutting depth/radial cutting depth). This is to avoid excessive bending of the tool handle/cutting tool and keep the processed mold with small tolerance and high precision

it is also very important to choose a clamping system and tool with good rigidity. When using integral cemented carbide tools, use

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