Design it right, Buy it right!
There are several factors that enter into the pricing of swaging work. The key factors are material type (including hardness and workability), material size and wall thickness, amount of reduction, length of reduction, configuration and angle of transition, tolerances of finished work, and to some extent tooling, quantity and desired delivery. For the sake of this article, these points will address tubular work that is rotary swaged on the ends, and will omit die-closing and stationary spindle work, as these operations have additional variables needing considered. It is also important to note that swaging is not an exact science, its really more of an art. There are so many variables that enter into each particular item, that each job must be judged on its own merits. The intent of this article is to state the rational used for quoting. Even with this information, there are some items that really can not be estimated. Nonetheless we offer Firm, Fixed Price Quotations and hold those prices firm on a calendar year basis.
|Material type |
Rotary swagers can develop incredible amounts of compressive force. The answer to the question “Can this be swaged?” is always “yes”. The real question is “What will this look like after it has been swaged?”.
The material must be ductile enough to withstand the amount of reduction imposed by the dies. Typically, small amounts of reduction (up to 5%of starting diameter) can be achieved cold on harder materials (up to Rc 45) in thin walls (less than .05″) without cracking the material. Unfortunately, actual results will vary.
We have done a lot of work that theoretically could not be done, by applying decades of experience. The softer the material, the easier it will swage. Lower amounts of carbon, chrome, molybdenum and nickel will also allow for easier swaging. Alternate to cold swaging is hot swaging. This can be done if the end item does not have strict tensile requirements, or if it goes through a final heat treatment subsequent to the swaging. Surface finish and tolerance is also degraded in hot swages. As a rule of thumb, hot swaging typically doubles the cost of the process and adds to the lot set-up time and cost due to the additional labor requirements.
|Amount of reduction |
If the material is ductile enough to withstand the cold reduction, there is no limit to the amount of reduction that can be accomplished in one pass. The inside diameter will get progressively “grainier” in appearance with increased amounts of reduction. Swage folds (laps) will then begin to develop. These can then propagate into cracks if reduction is continued or if the item goes through a subsequent heat treatment with a quench.
Greater amounts of reduction on harder materials will require outside process intermediate anneals between multiple progressive swages. Each intermediate swage will double the initial cost as well as adding the cost of anneal and have an equivalent effect to lead time. An alternate to this would be to hot swage.
|Material size and wall thickness|
Typically, very thin wall material will not work as well as tubing with a medium wall. This is because there is not enough material to withstand the tendency of the inside diameter to “fold”.
Material with wall thickness above .125″ begin to require greater amounts of power (larger equipment and tooling) to accomplish cold reductions. If swaging is attempted with equipment that is too small, progressively slower feeds must be used to accomplish the work.
This not only has a direct impact on the cost of the operation, but can also result in cracking on materials that work harden easily. These materials must be swaged quickly to minimize the negative effects of work hardening. Again, an alternate to this would be to hot swage.
|Length of reduction|
This is a time vs. money attribute. Once the process is in control, a swage that is twice as long as the basis, will cost twice as much to produce.
|Configuration and angle of transition|
The included angle of the swage reduction contributes significantly to the degree of difficulty of the swaging operation. This difference is exponentially increased with the amount of reduction. The forces generated in swaging needs to be put to work to reduce the diameter. Vectoring of these forces occurs with the inclusion of the angle. In essence, if there were a 45 degree angle, one half of the force applied to the part would be redirected into a longitudinal direction, trying to push the part out of the dies. This must be overcome by the feeding force generated by the ram.
There are significant limitations to this. Along with this is that steeper angles result in degradation of the surface finish of the reduced diameter section. Both of these can be improved to a degree by specifying generous corner radii on both sides of the transition.
|Tolerances of finished work|
Once the job is set-up, tolerance on diameters can be held consistently within .002″. This allows a drawing callout of +.010″ as a standard tolerance. Tighter tolerances can be maintained with an exponential increase in cost.
Length callouts are typically +.030″. This allows sufficient room for good production throughput. Again, tighter tolerances can be held, but contribute to increased costs.
|Tooling, quantity and delivery|
If enough flexibility exists in the design to utilize existing tooling, substantial money can be saved.
We have hundreds of dies on the shelf. Since the desired form must be put into a piece of tool steel, heat treated and ground, lead time as well as cost are affected. Engineering and tooling charges start at $200 for very small, very simple dies and have run to over $12,000 for complex, multistage dies.
Dies require storage and constant maintenance. For this reason, we do not build dies for customers, only for ourselves. Any charges paid for these are related to the engineering of the die. Dies remain the property of Master Swaging and we agree to keep up the die maintenance or replacement at our cost as long as we have the production associated with them.
In instances where small quantities of parts are needed, there are things that we can do to help avoid engineering costs, however if the job were to turn into a longer term project, it becomes more cost effective to produce a set of dies made specifically for the part as cycle times can be reduced by using a tool made for the job.