Mold making refers to processing of molding and blanking tools, also includes shearing dies and die-cutting dies. Usually, mold consists of an upper mold and a lower mold. Steel plate is placed between upper and lower molds, and material is formed under action of press. When press is opened, workpiece determined by mold shape is obtained or corresponding waste is removed. Workpieces as small as electronic connectors and as large as car dashboards can be formed by molds.

 

Progressive die refers to a set of molds that can automatically move workpiece from one station to another and obtain a molded part at last station. Mold processing processes include: cutting dies, blanking dies, compound dies, extrusion dies, four-slide dies, progressive dies, stamping dies, die-cutting dies, etc.

(1) Metal stamping molds: continuous molds, single-punch molds, compound molds, and stretching molds
(2) Plastic molding molds: injection molds, extrusion molds, and vacuum molds
(3) Die-casting molds
(4) Forging molds
(5) Powder metallurgy molds
(6) Rubber molds

Material cutting: front mold material, rear mold material, insert material, position material, and lifter material;
Frame cutting: front mold base, rear mold base;
Roughing: front mold cavity roughing, rear mold cavity roughing, and parting line roughing;
Copper electrode: front mold copper electrode, rear mold copper electrode, and parting line corner copper electrode;
Wire cutting: insert parting line, copper electrode, and lifter pillow position;
CNC: fine CNC parting line, fine CNC rear mold core;
Electric spark: front mold roughing, copper electrode, male mold line corner cleaning, rear mold bone position, Pillow position;
Drilling, pinhole, ejector; mold ejector hole waterway hole processing slide, slide pressure pole;
Lifter, double ejector, matching ejector.

 

(1) Nozzle, code mold pit, garbage nail (limiting nail);
(2) Fitting mold;
(3) Water inlet, support head, spring, water transport;
(4) Mold polishing, front mold, rear mold bone position;
(5) Fine water structure, pull rod screw hook, spring
(6) Heat treatment, quenching, slide surface nitriding of important parts;

UGNX, Pro/NC, CATIA, MasterCAM, SurfCAM, TopSolid CAM, SPACE-E, CAMWORKS, WorkNC, TEBIS, HyperMILL, Powermill, GibbsCAM, FEATURECAM, etc.

(1) High processing accuracy requirements. A mold is generally composed of a die, a punch and a mold base, and some may be multi-piece modules. Therefore, combination of upper and lower molds, combination of insert and cavity, and combination of modules all require high processing accuracy. Dimensional accuracy of precision molds often reaches μm level.
(2) Complex surface. Some products such as automobile covers, aircraft parts, toys, and household appliances have a surface composed of a variety of curved surfaces. Therefore, mold cavity surface is very complex. Some curved surfaces must be processed using mathematical calculation methods.
(3) Small batches. Production of molds is not mass-produced. In many cases, only one pair is produced.
(4) Many processes. Milling, boring, drilling, reaming and tapping are always used in mold processing.
(5) Repeated production. Use of molds has a lifespan. When a mold exceeds its lifespan, it must be replaced with a new mold, so production of molds is often repetitive.
(6) Sometimes there are no drawings or data in production of profiling molds, and profiling must be performed based on actual object. This requires high precision and no deformation.
(7) Excellent mold materials and high hardness. Main materials of molds are mostly made of high-quality alloy steel, especially long-life molds, which are often made of Crl2, CrWMn and other ledeburite steels. This type of steel has strict requirements from blank forging, processing to heat treatment. Therefore, preparation of processing technology cannot be ignored, and heat treatment deformation is also a problem that needs to be taken seriously during processing.
According to above characteristics, processing requirements should be met as much as possible when selecting machine tools. For example, CNC system should have strong functions, machine tool should have high precision, good rigidity, good thermal stability, and profiling function.

(1) Bottom surface processing, processing volume guarantee;
(2) Casting blank datum alignment, 2D, 3D surface allowance inspection;
(3) 2D, 3D surface rough processing, non-installation and non-working surface processing (including safety platform surface, buffer installation surface, pressure plate surface, side datum surface);
(4) Before semi-finishing, side datum surface alignment to ensure accuracy;
(5) Semi-finishing 2D, 3D surface, finishing of various installation working surfaces (including stop block installation surface and contact surface, insert installation surface and backrest surface, punch installation surface, scrap cutter installation surface and backrest, spring mounting surface and contact surface, various stroke limiting working surfaces, wedge mounting surface and backrest), semi-finishing various guide surfaces and guide holes, leaving allowance for finishing process reference holes and height reference surfaces, and recording data;
(6) Inspection and review of machining accuracy;
(7) Bench work process;
(8) Before finishing, align process reference hole reference surface and check insert allowance;
(9) Finishing of 2D and 3D profiles, side punch profiles and hole positions, finishing of process reference holes and height references, finishing of guide surfaces and guide holes;
(10) Inspection and review of machining accuracy.

(1) Process should be concise and detailed, processing content should be expressed numerically as much as possible;
(2) Process should be particularly emphasized at the key and difficult points of processing;
(3) Process should be clearly expressed at points where combined processing is required;
(4) When insert needs to be processed separately, pay attention to process requirements for processing accuracy;
(5) After combined processing, insert parts that need to be processed separately should be installed with benchmark requirements for separate processing during combined processing;
(6) Spring is the most vulnerable to damage during mold processing, so mold springs with long fatigue life should be selected.

 

When processing large molds, how to deal with their own huge size and weight is a major challenge faced by processing companies. Processing of large molds often requires a lot of labor, special equipment and multiple debugging and clamping, and processing accuracy is also affected by many potential factors and is not easy to guarantee.

The largest cost directly related to processing and production of various large molds is purchase cost of machine tools. Machine tools that can produce large molds are quite expensive, especially under complex process arrangements, multiple machine tools are needed to complete all processes from mold roughing to finishing. Such high initial investment costs are also the biggest obstacle for many companies to enter this market. From this, we can see that if large molds can be roughed and finished on a suitable machine tool, or even only require one debugging and clamping, many problems will be solved and machining accuracy can be guaranteed.

Cast iron material has high rigidity and heat dissipation characteristics, so it is the most stable material for manufacturing machine tool structural parts. For any machine tool used for milling large parts, it is first necessary to have a very strong cast iron structure and be equipped with a spindle with heat dissipation function.
As for spindle of machine tool, it must use built-in cooling technology to cool spindle from outside of bearing to ensure that spindle itself will not be burned or lose accuracy due to thermal expansion during long-term processing. These factors are very important because processing of large molds takes a long time, and under heavy cutting conditions, this will increase heat and stress of mold. Therefore, structural components of machine tool must have good rigidity and heat dissipation characteristics, which is premise for processing large and high-quality molds. Therefore, vibration of machine tool during processing must be limited to the greatest extent, and heat generated during processing must be quickly diffused. Choosing right processing machine tool and tool can achieve a win-win situation in terms of cost and cycle.

Due to long processing time, influence of ambient temperature must also be considered. For example, when processing large molds on ordinary machine tools, when ambient temperature changes by 10℃, temperature of machine tool column will change by 6℃, causing parallelism of spindle angle plate to change by 0.07mm. Therefore, design of machine tool must take into account effect of ambient temperature to avoid ambient temperature affecting accuracy of processed parts.

For a large mold processing center with a fast travel, spindle speed of large mold processing machine tool should be at least 20,000r/min, metal cutting speed should meet 762~20,000mm/min.

Precision control is always carried out throughout all stages of mold processing. If it is necessary to achieve rough machining and finishing of large molds on a machining center, positioning accuracy and repeat positioning accuracy of machine tool must be strictly controlled. Positioning accuracy of machining center dedicated to large molds can generally reach ±1.5μm, and repeat positioning accuracy should reach ±1μm. At the same time, its pitch accuracy should be kept within 5μm.

For high-precision surface processing, feedback resolution of machine tool itself is very important for detecting accuracy of processed parts. With standard 1μm feedback resolution, results usually obtained are not very ideal. If resolution can reach 0.05μm, then finishing result is almost flawless. In addition, processing quality of part surface can be further improved by controlling machine tool resolution, scale feedback and small pitch ball screw.

Spindle used in large mold machining center must meet requirements for rough machining, semi-finishing and high-quality finishing, and as a reference standard, surface processing quality that can be achieved should be controlled at level of 2μm. Generally, finishing of mold closing surface and parting line is very important, but under traditional processes, many mold manufacturers have to use manual polishing to compensate for problem of insufficient tool processing accuracy. Because large-scale processing machine tools are expensive, it is obviously impractical to purchase multifunctional machine tools for this process.
In addition, a reasonable spindle design must be able to maximize service life of tool so that it can continue to work in a state of low vibration and low temperature rise during processing cycle. For example, when processing an automobile dashboard mold on a large mold processing center, if a 16mm CBN insert finishing tool is used, processing speed can reach 8m/min, service life exceeds 30h, and processing surface quality can be controlled at 0.336~3.2μm. It can be seen from this that considering increase in tool costs when processing large molds, use of specially designed large mold processing machine tools can not only extend tool life, but also save a lot of tool use costs for processing each mold.

 

Due to limitations of mold size and weight, it generally takes a long time to clamp workpiece. Therefore, use of a 3-axis machining center not only reduces number of workpiece debugging and clamping times, but also does not affect machining accuracy of machine tool, thereby greatly improving workshop's production capacity for processing large molds.
Movable multi-axis machining head can be used to process large molds with particularly complex structures. Machining head designed with variable geometry allows 3-axis machining. Only one clamping of workpiece is required to mill molds with deep cavities and cooling holes, as well as many other parts with complex geometries. For example, when spindle is tilted at optimal angle, proximity of machining head to milling processing point can be increased, so that multi-axis machining head can be used to complete processing of inclined holes.
In addition, since multi-axis machining head uses radius blade of tool instead of tool tip when machining workpiece surface, surface roughness can be improved.

A large amount of chips will be generated during metal cutting. If they cannot be removed in time, secondary cutting will inevitably result, as well as temperature rise of machine tool structural components or workpiece surfaces. There are usually 18 chip removal holes under workbench of a large mold processing center, which can reliably remove chips no matter where workbench moves. There are 4 built-in hinged chip conveyors on machine tool, which transport chips to the front of machine tool at a very high speed.

High-pressure coolant plays a very important role in large mold processing. For example, when drilling inclined holes using the 2+3 axis processing method, a coolant with a pressure of 1000psi (1psi=6890Pa) is required to effectively remove chips and achieve higher precision cutting. If there is no such high-pressure coolant, additional machine tools need to be added when processing inclined holes, which requires secondary clamping, reduces processing accuracy, and increases cycle costs. According to above analysis, it can be seen that machine tool needs to have more and better functions to achieve simple processing of large molds.
New MCC2516VG3-axis horizontal machining center developed by Makino has a spindle speed of up to 15,000r/min, adopts "core cooling" method and "bearing internal pressure lubrication" function to ensure that spindle and its auxiliary bearings can be cooled in a timely and effective manner.
In addition, spindle can not only move along horizontal X-axis, vertical Y-axis and front-to-back Z-axis, but also rotate with A-axis and C-axis. Because it has two indexing functions, it can not only reduce adjustment workload, but also cut complex workpieces such as bumpers, dashboards and car headlight lenses.