What are the requirements of high-speed bottom die machine for processing materials when processing knife dies?

High-speed bottom die machine (commonly used for precision milling and engraving of cutter dies and dies, the core of which is to drive the cutter to cut the material with high precision through high-speed spindle) needs to focus on four core objectives of "machining efficiency, precision stability, cutter adaptability and finished product performance" when machining the cutter dies, so as to avoid machining defects (such as edge collapse and deformation) caused by material characteristics and ensure that the finished cutter dies can meet the subsequent use requirements (such as The following is a detailed analysis of the specific requirements from three dimensions: physical characteristics, chemical characteristics and morphological specifications of materials:

First, the core requirements: high-speed machining with material physical characteristics.

The spindle speed of high-speed bottom die machine is usually 10,000-40,000 rpm, with fast cutting speed and concentrated impact force. The physical characteristics of materials directly determine the machining stability and finished product accuracy. The core requirements include:

1. Hardness and strength: both "easy cutting" and "durable finished products"

In high-speed machining, the hardness of the material should match the hardness of the tool (such as cemented carbide tool HRC 60-70), so as to avoid cutting deformation caused by too hard cutting and too soft cutting;

Recommended range: Brinell hardness (HB)80-250 (or Rockwell hardness HRC 0-30), common materials such as medium carbon steel (45# steel, HB 190-230), aluminum alloy (6061-T6, HB 95-110), acrylic (HB 80-90) and bakelite (HB).

Prohibit/use materials with caution:

Excellent materials: such as high carbon steel (T10 steel, HRC 50+) and stainless steel (304, HB 180-200, but with high toughness), which may easily lead to tool edge collapse and excessive spindle load during high-speed cutting (which may lead to spindle failure);

Too soft materials, such as soft PVC(HB 50-60) and foamed plastics, are prone to "sticking to the tool" (the material is attached to the tool) and the edge is rough, which can not guarantee the precision of the cutting edge of the tool die.

2. Stiffness and deformation resistance: avoid dimensional deviation after processing.

High-speed cutting will produce local thermal stress and cutting force. If the material is not rigid enough, it is easy to have "deformation during machining-springback after cooling", which will lead to the out-of-tolerance of the die size (such as the deviation of the blade spacing);

Key indicators: elastic modulus (E)≥20GPa (to measure the deformation resistance of materials);

Qualified materials: 45# steel (E≈200GPa), aluminum alloy (6061, E≈69GPa), phenolic resin plate (bakelite, E≈15GPa, cutting parameters should be controlled when approaching the lower limit);

Unqualified materials: cork board (E≈0.3GPa) and rubber board (E≈0.01GPa), which are easy to be "pushed and deformed" by the cutter during processing, and cannot form accurate groove position or cutting edge of the cutter die.

3. Density and uniformity: ensure the stability of cutting force

Uneven internal density of materials (such as impurities, bubbles and texture differences) will lead to "sudden change of cutting force" during high-speed cutting, which will lead to tool vibration and further affect machining accuracy (such as excessive surface roughness);

Requirements: density fluctuation ≤5%, no obvious impurities, bubbles and stratification;

Typical case:

Qualified: industrial acrylic board (density 1.19 g/cm, uniform and bubble-free) and homogeneous bakelite board (no resin caking);

Unqualified: Plastic board (containing impurity particles) and natural wood (uneven texture density) pressed by recycled materials are prone to "edge collapse" (lack of edge angle) and "tool jumping" (different depth of groove caused by instantaneous deviation of tool) during high-speed cutting.

4. Thermal stability: resistance to deformation caused by cutting heat.

When cutting at high speed, the friction between the tool and the material will produce local high temperature (up to 200-500℃). If the thermal expansion coefficient of the material is too large or the heat resistance is poor, the machining dimension deviation will be caused by thermal deformation:

Key indicators: linear expansion coefficient (α) ≤ 20× 10/℃ (25-100℃), heat-resistant temperature ≥ 150℃;

Recommended materials: 45# steel (α ≈ 11× 10/℃, heat resistance ≥500℃), aluminum alloy (6061, α ≈ 23.6× 10/℃, close to the upper limit but fast heat dissipation);

Caution material: ordinary PVC board (α ≈ 50× 10/℃, heat resistance ≤80℃), which is easy to soften and stick to the knife at high temperature during high-speed cutting, and shrinks after cooling, resulting in the reduction of the size of the knife die.

Second, secondary requirements: chemical characteristics and processing adaptability

Although the chemical characteristics of materials do not directly determine the machining accuracy, they will affect the tool life, machining environment and the applicability of finished products. The following requirements should be met:

1. Low "tool affinity": avoid sticking and wearing the tool.

Some materials are easy to react with tool materials (such as tungsten steel and high-speed steel) at high temperature, or adhere to the surface of the tool due to stickiness, resulting in "tool sticking" (affecting cutting fluency) and "chemical wear" (shortening tool life);

Recommended materials: steel, aluminum alloy, acrylic (good chemical stability, no obvious affinity with tools);

Use materials with caution:

Copper alloy (such as brass, containing zinc): zinc is easy to react with tungsten steel tools during high-speed cutting, resulting in "coating peeling off" on the tool surface;

Soft plastics (such as PE, PP): high viscosity, easy to stick to the cutting edge of the tool, need to stop frequently to clean, reduce processing efficiency.

2. Low dust/low volatilization: ensure the processing environment and equipment safety.

When cutting some materials at high speed, it will produce a lot of dust (such as bakelite and wood) or toxic volatiles (such as inferior PVC), which not only pollutes the environment, but also may block the dust collection system of equipment and damage the health of operators;

Requirements:

Dust is easy to collect: for example, acrylic cutting dust particles are large and difficult to fly, which can be effectively removed by negative pressure vacuum cleaning;

No toxic volatilization: Avoid using inferior resin plate containing formaldehyde and benzene (such as non-national bakelite), and give priority to environmental protection materials (such as E0 phenolic resin plate).

III. Basic Requirements: Equipment for Adapting Material Form and Specification

The initial shape and size of the material should be matched with the processing range and clamping mode of the high-speed bottom die machine, otherwise it can't be processed stably;

1. Smoothness: avoid "datum deviation" after clamping.

High-speed bottom die machine usually locates based on the "bottom surface" of the material. If the flatness of the material is poor (such as warping and depression), after clamping, it will lead to "the machining surface is not perpendicular to the spindle", and then the depth deviation of the die will appear:

Requirements: the flatness error within each meter length is ≤0.5mm (which can be detected by level ruler);

Frequently asked questions: Thin acrylic board (thickness ≤3mm) is prone to warping due to transportation extrusion, and needs to be corrected by flattening machine in advance before processing.

2. Dimensions and specifications: match the processing stroke and clamping range of the equipment.

Thickness range: it should match the "Z-axis stroke" of the equipment (usually the Z-axis stroke of high-speed bottom die machine is 50-200mm, and the material thickness should be ≤ 80% of the stroke to avoid insufficient tool stroke);

Length and width specification: it should match the "workbench size" of the equipment (for example, the workbench is 1200×600mm, the material length and width should be ≤1100×500mm, and the clamping space should be reserved);

Edge verticality: the verticality error of the "length× width" section of the material is less than or equal to ≤0.1mm/m/m, so as to avoid machining coordinate deviation caused by edge inclination during clamping.

3. Surface condition: no surface damage will affect the positioning.

The surface of the material shall be free of obvious scratches, oil stains and oxide layers (such as severe oxidation on the surface of aluminum alloy);

Scratches/depressions: it will lead to "uneven datum plane" during clamping, which will affect the machining depth accuracy;

Oil stain/oxide layer: it will affect the stability of "vacuum adsorption clamping" (vacuum chuck is commonly used to fix materials for high-speed bottom die machines), and material may slip during processing, which may lead to safety accidents.

Fourth, examples of material selection for different die types

In combination with the above requirements, materials should be selected for different knife dies (such as cutting knife dies and stamping knife dies), as shown in the following table:

Core requirements of die type Recommended materials Prohibited/Carefully used materials

Carton/film cutting die has the advantages of easy machining and low cost, such as bakelite (thickness 5-15mm), acrylic high carbon steel (difficult to cut) and soft PVC (easy to deform).

The finished metal sheet stamping die has high rigidity and wear resistance. 45 # steel (processed before quenching, HB 200-230), aluminum alloy (insufficient strength) and foam plastic (no rigidity).

Cutting dies for precision electronic parts (such as FPC) have high machining accuracy and no deformation. 6061-T6 aluminum alloy (surface anodizing) recycled materials are bakelite (uneven density) and wood (texture affects accuracy).

Summary: the core logic of high-speed bottom die machining materials

The essence of high-speed bottom die machine's requirements for materials is "the matching of material characteristics and high-speed machining technology"-not only to make materials "efficiently and accurately cut" by high-speed tools (to avoid damaging equipment and tools), but also to make the finished die meet the requirements of "dimensional accuracy and durability". In actual selection, it is necessary to make clear the subsequent use of the die (such as cutting material and frequency of use), and then combine the equipment parameters (spindle speed and stroke) to select materials from the four dimensions of "hardness, rigidity, uniformity and specification", so as to finally achieve the goal of "high processing efficiency, high qualified rate of finished products and low equipment loss".