The powder warm compacting process is put hot mixed material into the hot closed steel mould compacting with pressure.The temperature of warm compacting is usually 110-150℃. Because the press temperature is between usual room temperature and hot pressing temperature,thus it called warm-press. The correct warm-press process can improve the density of iron green parts from 6.6~6.8g/cm in room temperature((600~800MPa) to 7.25~7.45g/cm, and the cost of process is lower than complex pressure, complex burning, infiltration of copper, hot forging. So, The ANCORDENSE process as the representative of the warm pressing forming technology known as the 90's iron and steel powder metallurgy parts production process a major breakthrough.
The factors of influence the warm-pressure forming process have correct parts design, suitable powder system, correct choose of powder and tools, and reasonable tool material and tolerance fitting.
The design of parts is reduce the friction bettween powder and tool wall caused by rising temperature, it must noted influence of powder loading height with to be pressed powder.
The one of Parameter reflecting this influence is the ratio of side pressure area to pressing area, defined to temperature compression side pressure coefficient.The researches shown that the warm-pressure is better suit to produce powder metallurgy parts with height-diameter ratio H/D≤1 in same process situation. But for larger height-diameter ratio,it must use any other lubricting way, such as outside lubrication.
The powder warm compacting process have strictly raw stainless steel powder requests.Usually, it use highly compressible powder,Oxygen content <0.1%, Carbon content <0.01%, Nitrogen content <0.0013%, Acid insoluble matter <0.1%, Bulk density: 2.90-3.00g / cm.Added graphite will reduce density of green parts.For pre-alloyed powders containing molybdenum and nickel and partially pre-alloyed powders, the warm-pressure process is effective.But for sintered hardening powder, in particular, manganese, chromium and other alloying elements of the series of powder,some process need to be improved.
The features of lubricant warm-pressure have a certain liquidity and don't influence the liquidity that the mould need.
The best material of lower mould is hard-alloy. In warm temperature, the hard-alloy have high wear resistance, heat resistance and dimensional tolerances. When the temperature of moul is achieve 100~180℃, the negative cemented lining can be cooled for some time at liquid nitrogen temperature, let it shrinkage to certains dimensions, and then put into lower mould case in room temperature.When the temperature of the cemented carbide liner returns to room temperature, a volumetric expansion occurs to form a sufficient compressive stress of the liner on the liner.
The base way of heating powder and mould is oil heating and electronic heating.The temperature choose is importance process parameter of warm-compacting.To determine the temperature and pressure of several principles:
(1)Large-scale, high powder loading powder compact temperature should be lower than the pressure of small-size compact temperature
(2)To make all the oozing oozing compacts, especially for the small compact powder filling height, the mold temperature should be higher than the powder temperature
(3)Temperature and pressure can be higher than the temperature of the glass transition temperature of the lubricant 25 ~ 85 ℃, so that the lubricant was semi-fluid state
The warm-compacting can use ordinary press machine,just do some improve for mould and feed mechanism. In foreign, they had developed special warm-compacting press machine, its high self-control and good product consistency.
Because the warm-pressing process can get the high density and trength use lower pressing pressure, and it can produce big components use currently press machine. At the same time, increase the density of green compact, can make the original must be sintered after processing such as drilling blind holes and turning threads in advance after pressing. It will big reduce the difficulty of post machining, improved production effiective.The warm-compacting process opened up a new low-cost process line for high-strength iron parts in automotive application. Thus,The technology has aroused people's high attention, is being constantly improved and improved.
