… At this point, we have located two presses that seem to match our needs, one being a screw press and the other a mechanical press. We need to consider different ways to forge these parts so that there is little or no unplanned machining or conditioning required after forging. Our production process involves machining a small notch on one end and a small hole in the other end of the part, but we prefer not to perform any further operations (other than coating.) What do you advise?
A: First of all, the stronger alloys of 7075 and 7050 can be forged in each machine. The only problem you might face with a screw press is excessive adiabatic heating if the hot plastic reductions are rather high and the forging temperature is too close to the solution treatment temperature. However, this should not be a problem with your parts because you are planning to bend the blanks first, followed by forging in one or two blows depending on the particular part being forged.
The mechanical press you are considering is called a knuckle press. For low-profile parts this kind of press is quite good and they generally cost much less than either the screw press or a similar, mechanical pitman-type crank forge press. The knuckle press is not used for tall or deep parts, because the working stroke is limited to the final 1-2 in. of stroke where the loads are reaching press capacity.
Also, the stroke is limited, it is unwise to use a kissing surface on the dies because this could cause a wreck or a lockdown of the knuckle-style presses. Be aware that the forgings might require a coining operation (probably cold) to deliver the thickness tolerances you are seeking.
For more than 40 years H. James Henning held key technical positions in the forging industry, including as director of technology for the Forging Industry Association, and as president of Henning Education Services, a Columbus, OH, firm specializing in customized education and training in forging technologies.
Guidelines and recommendations offered in this column are based on information believed to be reliable and are supplied in good faith but without guarantee. Operational conditions that exist in individual plants and facilities vary widely. Users of this information should adapt it, and always exercise independent discretion in establishing plant or facility operating practice.