Molding is a method suitable for mass production of high-quality, small and medium-sized fiber reinforced products. The cold pressing forming process and the hot pressing forming process are described below.
First, what is the cold pressing forming process?
Cold pressing is an intermediate process for the transition from contact forming to hot pressing. The mould used in the cold pressing process is a FRP mold; the hydraulic press also belongs to the lightweight grade; the molding pressure generally does not exceed 0.5MPa.
In cold pressing molding, because of resin curing heat release, the mold can reach 40 ℃ 50 ℃, and the local temperature can reach 60 ℃ 70 ℃. In order to produce products of constant quality, the mold is often heated first at the beginning of production, and the curing heat release is used to heat the mold after the temperature is stable, so that the forming cycle is shortened.
The mould is commonly made of FRP, with an average life of 1000 times and 2000 times. In order to ensure that the mold does not deform in use, the mold is generally installed on the steel frame and backed by pressure-resistant materials, such as resin mixture of sand and stone powder filled with concrete. In the design of the die, the extruded fiber should be extruded on the edge of the die, so that the gas in the die can overflow and the resin can be retained, and the gap in the extrusion zone should be able to extrude the thickness of the two layers of felt. Unlike hot-pressing moulds, excess fibers can be removed.
What is the hot pressing process?
Hot pressing is the most economical method for mass production of medium and small products. The surface of the product is smooth and can meet the requirement of high tolerance. However, the investment cost of equipment and mould is large, so it is not suitable for the production of products with changeable varieties and specifications and small batches.
The mold is a matching metal-to-die, installed on the hydraulic press, with automatic opening, closing and accurate speed control.The die length is made of tool steel with quenched edges. The compression cycle can be controlled by computer. The trimming of the edge of the product can be completed automatically. For the molded parts of liquid resin and preformed fiber, the device demoulding device does not need to be set on the mold, but for SMC products, the ejection device can be set up. The surface of the mold should be highly polished and can be plated with chromium. The service life of the die can reach 1 million times. In order to prevent the product from warping, the maximum temperature difference on the surface of the die should not exceed 2.5 ℃.
Release agents can be organosilane, but after the normal operation of the mold, internal release agents can be used for SMC and BMC. If the products still need to be painted, the release agents must be carefully selected, and the silicone release agents that hinder bonding can not be used.