How to make extrusion blow moulds?
Machining and casting are the two most common methods to manufacture the mold cavity.Which method is used depends on a variety of factors, such as mold material, number of mold cavities, complexity of cavity and precision requirements of cavity.
Mold material is the most important factor in determining manufacturing method.Aluminum is harder to cast. Only certain kinds of aluminum can be cast.Generally speaking, aluminum alloy with high silicon content is most suitable for casting, while aluminum alloy with high strength cannot be cast and should be machined.Copper beryllium alloy mold has good performance.Most steel molds are machined and manufactured, while zinc alloys are easy to cast.
If the cavity number is large, cavity complex or irregular, cavity size tolerance requirements are low, cavity volume is large or production volume is less, casting method can be used to manufacture the mold.The cost of casting die is low, but its durability and thermal conductivity are lower than those of machining die.Some special casting methods can be used to produce high performance molds. For example, pressure casting method can reduce the porosity of aluminum and copper beryllium alloy and guarantee the high precision of the mold cavity.The machining methods of the blow mold cavity mainly include milling, grinding, etc.
There are also cold extrusion, hot extrusion, edm and welding methods.The cold extrusion method is suitable for small moulds, especially for multi-cavity moulds, to ensure the consistency of each cavity.For large volume (such as 3m3) cavities, machining and welding methods can be used to manufacture them.When high dimensional accuracy is required, the mold cavity shall be manufactured by copying milling.
The shrinkage must be taken into account when designing the cavity size.For machining cavity, shrinkage includes shrinkage of blow molding products and shrinkage after mold processing.For the casting cavity, the shrinkage rate in the casting process should also be considered.
The final stage of cavity manufacturing is polishing, sandblasting or etching.Before etching, especially when it is necessary to etch fine patterns, the scale and marks generated by cutting, edm, grinding or extrusion should be removed to ensure a certain degree of finish.Mold cavities are generally not hardened and rarely plated with metal (e.g., chromium) unless they are produced in large batches.If the cavity is to be hardened or chrome plated, it should be done after etching.
Clamping billet inlay, pull rod, guide column and guide sleeve, etc. Most of steel or copper beryllium alloy through mechanical processing, but also through hardening.