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What issues, exactly, require the most attention during the manufacturing and assembly stages of large injection molds?

I. Lifting Safety: The Prerequisite for Everything

The assembly of large molds first confronts the issue of lifting. Multi-ton mold bases and cavities—if improperly lifted, the consequences can be disastrous.

Lifting operations are governed by strict standards. Molds weighing over 10 tons must use two wire rope slings with four lifting rings in a double-lift configuration, and each shackle used must have a load capacity of no less than 10 tons. The depth to which the lifting ring is screwed into the mold must be greater than 1.5 times the ring's diameter. If the ring surface does not sit flush against the mold, shims must be used to prevent the ring from bending and breaking. Lifting should begin slowly—never with a sudden, rapid hoist. The mold should be kept below 80mm from the ground, and only raised after it has been moved in front of the machine and stabilized. Operators must maintain a horizontal distance of at least 1 meter from the mold, and standing beneath a suspended mold is strictly prohibited.

More importantly, the lifting apparatus must always remain above the center of gravity. If the suspension point deviates from the center of gravity, the entire system will tilt during lifting until the center of gravity settles below the suspension point—and the swaying during this process can easily cause mold collisions or personnel injuries.

II. Unified Datum: The "Root" of Precision

Datum deviation is the fundamental source of assembly misalignment and abnormal fitting clearances in mold components. For large molds with many parts and significant cumulative errors, the importance of datum unification is even more pronounced.

Throughout the entire process—from machining, grinding, and fitting to assembly—the same datum corner and datum surface should be used consistently, and mixed datums are prohibited. All machining, inspection, and assembly dimensions should be based on the mold datum to eliminate cumulative datum deviations. Excessive milling and grinding errors on the datum corners, datum planes, and guide pillar datum surfaces of mold base plates A and B—where flatness, perpendicularity, and parallelism exceed tolerances—will cause all subsequent inserts, sliders, and cavity assemblies to shift. Therefore, the tolerance for all datum surfaces should be controlled within 0.01mm. The positional tolerance of guide pillar holes, locating pin holes, and insert locating datum holes should be ≤0.015mm to eliminate assembly misalignment caused by hole position deviation.

III. Assembly Sequence and Cleanliness: Details Determine Success or Failure

Assembly should follow the principle of "inside first, outside later; small first, large later"—first assembling the core and cavity, then the guide pillars and guide bushings, and finally the ejection mechanism. Before assembly, parts must be cleaned of metal chips, oil, and dust to prevent impurities from entering fitting clearances and causing poor sliding or wear. Avoid striking parts forcefully during assembly; when tapping inserts, use a nylon rod or copper bar as a buffer and tap gently to prevent deformation or damage.

The image below shows a mold assembly photo from Haina Company's factory. With years of mold processing experience and exposure to many types of molds, Haina Company is highly trustworthy in terms of professionalism.

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IV. Fitting of Critical Mating Surfaces: The Embodiment of Craftsmanship

The fitting of large molds requires adherence to specific technical principles. For the cavity, the large-end dimension should be kept within the tolerance range of the part; for the core, the small-end dimension should be kept within the tolerance range of the part. When a mold has both horizontal and vertical parting surfaces, the vertical parting surface should be in contact while the horizontal parting surface retains a slight clearance—approximately 0.02mm for large molds. For molds that clamp via inclined surfaces, after the inclined surfaces mate, a clearance of 0.02–0.03mm should be left at the parting surface. The red lead contact area within 15mm around the PL surface should reach 95% or more, and the red lead contact area within 15mm behind the venting grooves should be 70% or more.

V. Tolerance Analysis and Assembly Precision Optimization: From Experience to Science

Large molds consist of hundreds of components, and tolerance accumulation can significantly affect assembly precision. Traditionally, this relied on the judgment of experienced masters. Today, tolerance allocation methods based on block assembly are being introduced—research shows that this approach can reduce assembly tolerance from 0.071mm to 0.032mm and improve manufacturing defect rates from 9.05% to 0.02%. This means that manufacturing capability can be considered at the design stage, ensuring assembly precision through rational tolerance allocation while reducing manufacturing costs.

VI. Hot Runner System Installation: Details That Cannot Be Overlooked

If the mold uses a hot runner system, the following points require attention during installation: all connecting wires should use high-temperature-resistant wire rated for 300°C or above to prevent insulation melting and circuit breakage. Throughout the entire installation process, care should be taken to prevent metal chips and other foreign matter from entering the hot runner system, avoiding gate blockage during trial molding.

IV. Global Expansion Becomes a "Must-Answer Question"

Leading companies are accelerating their overseas expansion. Currently, Yizumi has established subsidiaries in 12 countries overseas, with a global service network covering nearly 180 service points. In the first half of 2026, China's cumulative export value of injection molding machines reached approximately 7.167 billion RMB. Chinese-made equipment, leveraging acceptable quality and competitive pricing, has performed notably well in markets such as Mexico, Vietnam, and Turkey.