When mold is opened, movable mold and fixed mold are separated to take out plastic part, which is called a single parting surface mold, also called a double-plate mold. It is the simplest and most basic form of injection molds. It can be designed as a single-cavity injection mold or a multi-cavity injection mold according to needs. It is the most widely used injection mold.

Double parting surface injection mold has two parting surfaces. Compared with single parting surface injection mold, double parting surface injection mold adds an intermediate plate (also called movable gate plate, which is equipped with gates, runners other parts and components required by fixed mold) that can be moved locally in the fixed mold part, so it is also called a three-plate (moving mold plate, intermediate plate, fixed mold plate) injection mold. It is often used for single-cavity or multi-cavity injection molds with point gate feeding. When mold is opened, intermediate plate is separated from fixed mold plate at a fixed distance on guide post of fixed mold, so that casting system condensate can be taken out between two mold plates. Double parting surface injection mold has complex structure, high manufacturing cost, and difficult parts processing. Generally, it is not used for molding of large or super large plastic products.

When plastic part has side holes or undercuts, it is necessary to use a laterally movable core or slider for molding. After injection molding, movable mold first moves down for a certain distance, then inclined section of bending pin fixed on fixed mold plate forces slider to move outward, and at the same time, push rod of ejection mechanism pushes pusher plate to remove plastic part from core.

Due to special structure of plastic parts, injection mold is required to be equipped with movable forming parts, such as movable punches, movable concave molds, movable inserts, movable thread cores or rings, etc., which can be moved out of mold together with plastic part during demolding, then separated from plastic part.

For plastic parts with threads, when automatic demolding is required, a rotatable thread core or ring can be set on mold, and mold opening action or rotation mechanism of injection molding machine can be used, or a special transmission device can be set to drive thread core or thread ring to rotate, thereby ejecting plastic part.

Runnerless injection mould refers to method of adiabatic heating of runner to keep plastic between nozzle and cavity of injection moulding machine in a molten state, so that there is no condensate in gating system when mould is opened and plastic part is taken out. The former is called adiabatic runner injection mold, and the latter is called hot runner injection mold.

Right-angle injection molds are only suitable for angle injection molding machines. Difference from other injection molds is that feeding direction of this type of mold is perpendicular to opening and closing direction of mold during molding. Its main runner is opened on both sides of parting surface of moving and fixed molds, and its cross-sectional area is usually constant. In order to prevent wear and deformation of nozzle of injection molding machine, inlet end of main runner, replaceable runner inserts can be provided at the end of main runner.

 

In most injection molds, demolding device is installed on the side of movable mold, which facilitates work of ejector device in opening and closing system of injection molding machine. In actual production, because some plastic parts are limited by shape, it is better to leave plastic part on the side of fixed mold for molding. This makes plastic parts eject from mold, and a demoulding mechanism must be set on the side of fixed mold.

Mold Making refers to processing of forming and blanking tools, in addition to cutting dies and die-cutting dies. Under normal circumstances, mold consists of two parts, an upper mold and a lower mold. Steel plate is placed between upper and lower molds, material is formed under action of press. When press is opened, workpiece determined by shape of mold will be obtained or corresponding waste will be removed. As small as electronic connectors, workpieces as large as automobile dashboards can be molded by molds.
Progressive mold refers to a set of molds that can automatically move processed workpiece from one station to another, get molded part at the last station. Mold processing technology includes: cutting die, blanking die, compound die, extrusion die, four slide rail die, progressive die, stamping die, die cutting die, etc.

(1) Metal stamping die: continuous die, single punch die, compound die, drawing die
(2) Plastic molding mold: injection mold, extrusion mold, blister mold
(3) Die casting mold
(4) Forging die
(5) Powder metallurgy mould
(6) Rubber mold

Cutting material: front mold material, rear mold material, insert material, row position material, inclined top material;
Open frame: front mold frame, rear mold frame;
Rough opening: front mold cavity is opened, back mold cavity is opened, and parting line is opened;
Copper male: front mold copper male, rear mold copper male, parting line clear angle copper male;
Wire cutting: insert parting line, copper male, inclined top pillow position;
Computer gong: fine gong parting line, fine gong back mold core;
Electric spark: front mold thick, copper male, male mold line clear angle, back mold bone position, pillow position; drilling, pinhole, thimble; mold thimble hole waterway hole processing position, position pressure pole; inclined top, compound thimble, with thimble.

(1) Chicks, code mold pits, garbage nails (limiting nails);
(2) Fitting mold;
(3) Nozzle, support head, spring, water transportation;
(4) Mold saving, polishing, front mold and back mold bone position;
(5) Thin water structure, pull rod screw hook, spring
(6) Heat treatment, quenching, and 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 pair of molds is generally composed of a concave mold, a convex mold and a mold base, and some may also be a multi-piece split module. Therefore, combination of upper and lower molds, combination of inserts and cavities, and assembly of modules require high machining accuracy. Dimensional accuracy of precision molds often reaches μm level.
(2) Complex shapes. Some products, such as car covers, aircraft parts, toys, and household appliances, have shapes and surfaces that are composed of multiple curved surfaces. Therefore, mold cavity surface is very complicated. Some curved surfaces must be processed by mathematical calculation methods.
(3) Small batches. Production of molds is not mass production. In many cases, only one pair is produced.
(4) Multiple processes. Milling, boring, drilling, reaming and tapping are always used in mold processing.
(5) Use of repetitive production molds has a long life. When use of a pair of molds exceeds its life, a new mold must be replaced, so production of molds is often repetitive.
(6) In production of profiling molds, sometimes there is neither pattern nor data, and profiling must be performed according to actual object. This requires high imitation accuracy and no deformation.
(7) Mold material is excellent, main material of mold with high hardness is mostly made of high-quality alloy steel, especially long-life mold, which is often made of ledeburite steel such as Crl2, CrWMn. This kind 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 in processing.
According to above-mentioned many characteristics, it is necessary to meet processing requirements as much as possible in selecting machine tool. For example, function of CNC system should be strong, precision of machine tool should be high, rigidity should be good, thermal stability should be good, and it has function of profiling.

 

(1) Bottom surface processing, guaranteed processing capacity;
(2) Alignment of casting blank datum, 2D and 3D surface allowance inspection;
(3) 2D, 3D profile rough machining, non-installation non-working plane machining (including safety platform surface, buffer mounting surface, pressure plate plane, side reference surface);
(4) Before semi-finish machining, side reference surface is aligned to ensure accuracy;
(5) Semi-finishing 2D, 3D surface, finishing all kinds of installation working surfaces (including limit block installation surface and contact surface, insert block installation surface and backside, punch installation surface, waste cutter installation surface and backside, spring installation surface and contact surface, various stroke limit working surfaces, inclined wedge mounting surface and backside), semi-finishing various guiding surfaces and guiding holes, leaving a margin for finishing process reference holes and height reference surfaces, and recording data;
(6) Inspection and review of processing accuracy;
(7) Fitter inlay process;
(8) Before finishing, align datum surface of process datum hole and check insert margin;
(9) Finishing profile 2D, 3D, side punch profile and hole position, finishing process reference hole and height reference, finishing guide surface and guide hole;
(10) Inspection and review of machining accuracy.

(1) Process preparation is concise and detailed, processing content is expressed numerically as much as possible;
(2) For key and difficult points of processing, craftsmanship should be particularly emphasized;
(3) It is necessary to combine processing parts, and process is clearly expressed;
(4) When inserts need to be processed separately, pay attention to process requirements of processing accuracy;
(5) After combined processing, for insert parts that need to be processed separately, process is equipped with benchmark requirements for separate processing during combined processing;
(6) Springs are most easily damaged in mold processing, so mold springs with long fatigue life should be selected.

When processing large molds, how to deal with its 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, multiple debugging and clamping, 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 tool. Machine tool that can produce large molds is quite expensive, especially in complex process arrangement, requiring use of multiple machine tools to complete all processes from roughing of mold to inishing. Such early high input cost is also the biggest obstacle for many companies to enter this market. From this, we can see that if rough machining and finishing of large molds can be realized on a suitable machine tool, even if only one debugging and clamping is required, then many problems will be solved and machining accuracy can also be guaranteed.

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

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

 

For a large mold machining center that can move quickly, spindle speed of large mold processing machine tool should reach at least 20000r/min, and metal cutting speed should meet 762~20000mm/min.

Precision control always runs through all stages of mold processing. If you need to achieve rough machining and finishing of large molds on a machining center, you must strictly control positioning accuracy and repeat positioning accuracy of machine tool. Machining center dedicated for large molds generally has a positioning accuracy of ±1.5um, and a repeat positioning accuracy of ±1um. At the same time, its pitch accuracy should be kept within 5um.

For high-precision surface processing, feedback resolution of machine tool itself is very important for detecting accuracy of processed parts. With standard 1um feedback resolution, results usually obtained are not very satisfactory. If resolution can reach 0.05um, then its finishing result is almost without any flaws. Moreover, processing quality of part surface can be further improved through control of machine tool resolution, scale feedback and small pitch ball screw.

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

Due to limitation of mold size and weight, it usually takes a long time to clamp workpiece. Therefore, use of a 3-axis linkage machining center not only reduces number of debugging and clamping times of workpiece, but also does not affect machining accuracy of machine tool, thereby greatly improving production capacity of workshop for processing large molds.
Movable multi-axis machining head can be used to process large-scale molds with particularly complex structures. Machining head designed according to variable geometry allows 3-axis simultaneous machining. It only needs to clamp workpiece once to mill deep molds and cooling holes, and cut many other parts with complex geometries. For example, when spindle is inclined at optimal angle, proximity of processing head to milling point can be increased, so that multi-axis processing head can be used to complete processing of oblique hole.
In addition, since multi-axis machining head processes surface of workpiece, radius edge of tool is used instead of tip of tool, so surface roughness can be improved.

A large amount of chips will be generated during metal cutting. If it cannot be eliminated in time, it will inevitably lead to secondary cutting and cause temperature rise of machine tool structural parts or surface of workpiece. There are usually 18 chip holes under worktable of a large mold machining center, no matter where worktable is moved, chips can be reliably removed. There are 4 built-in hinged chip conveyor belts on machine tool, which send chips to the front of machine tool at a high speed.

In processing of large molds, high-pressure coolant plays a very important role. For example, when using 2+3 axis machining method to drill inclined holes, 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, a second installation is required, which reduces processing accuracy and increases cycle cost. According to above analysis, it can be seen that simple processing of large molds requires machine tool to have more and better functions.
New MCC2516VG 3-axis horizontal machining center developed by Makino, spindle speed can reach 15000r/min, adopts "shaft core cooling" method and "bearing internal pressure lubrication" function to ensure that spindle, its attached bearings can be cooled in time and effectively .
In addition, main shaft can not only move along horizontal X axis, vertical Y axis, front and rear Z axis directions, but can also rotate with A axis and C axis. With two indexing functions, it can not only reduce workload of adjustment, but also cut complex workpieces, such as bumpers, instrument panels, and automobile headlight lenses.