7 Reasons Why Cycle Time Isn’t The Cost Driver In Your Precision Machined Parts

October 25, 2011

In the old days, everybody knew that it was cycle time that won you the job over the other shops…

Everybody knows it's cycle time...

Cycle time is a major determinant of price per piece, but it may no longer be the main one. (I’m going to ignore the effect of setup time and order quantity in this discussion. These can also be a major influence in price per piece on smaller lot sizes.)

Here are 7 other determinants of piece cost:

Cleanliness– some parts require millipore tests to assure cleanliness on parts for sophisticated systems. Costs to obain this level of cleanliness can exceed the cost to whittle the part out of the barstock.

Surface finish– what the machine can deliver may be acceptable, but when the customer demands to see CPK for surface finish,  now you are talking about a secondary operation for grinding, honing or other surface finishing process- at an additional cost.

Certifications and paperwork– No I’m not talking about mill certs for raw material, I’m talking about customer required documentation that requires outside labwork, analysis, testing or validation.  In specialty areas like aviation, medical, and automotive, the cost to prepare paperwork submissions (especially first piece submissions) easily exceeds the value of the parts provided. Making aircaft parts? Something on the U.S. Munitions List? You know what I’m talking about.

Post process steps– Plating or heat treating costs can exceed the cost of the basic part depending on the process and application. Transportation to outside vendors also adds to this, as would the compliance costs if the shop is capable of doing these processes on site.

Packaging– In a day when supply chains span the globe, multiple time zones, and climate regions- where our metal products may be exposed to salt air on board ship or depressurized air cargo holds at 35,000 feet- packaging to preserve product integrity can be a cost driver. Especially if to Mil-spec and or the requirement mandates the  need to preserve integrity for a period of years.

Tolerances and capability– I have seen parts where a new engineer has decreased the tolerance so much  that the product can no longer be made on the economical machines that exceeded requirements for the past five years. Requiring Cpk that exceed normal manufacturing expectations “just for safety’s sake” can also result in moving a part off a multispindle automatic with short cycle times onto  several CNC machines (to maintain volume) just to get that extra “kick” of Cpk. The risk that was eliminated is now reflected in the new cost of the more expensive process.

Raw Materials– on tiny, high stock removal, highly engineered parts, the cost of machining probably does exceed the cost component of the raw material. Show me a part that looks essentially like the piece it was made from, and I’ll show you a part where raw material cost, not cycle time, is the primary cost driver.

Transportation, including premium freight for parts or paperwork, is another item to consider. The point of this post is not to whine about all of these additional requirements- it is to point out that they can be a frictional cost, a parasitic load that increases part costs, and yet are under the control of the Buyer. These costs, either separately or in combination, may be the main drivers of why that 15 second  part now costs so much.

Sales people and estimators- unless you actively review the real needs with your customer, your blind acceptance/compliance to all of these “Additional Requirements” may be the real reason that the customer comes back saying that “Your price is too high.”

I teach my students that critical thinking is recognizing and challenging assumptions. Critical sales and estimating, if they are to be successful, might share that definition of recognizing and challenging those assumptions that add cost, but not value, to our precision machined products.

Stopwatch2


6 Ways Barstock Can Lose Straightness

September 16, 2009

Straightness is perishable in bars. Straightness is often lost during handling operations, loading and unloading.

Correct handling preserves straightness.

Correct handling preserves straightness.

Straightness is critical for holding position and tolerances on today’s highly engineered medical, aerospace, automotive and electronic parts.

Here are six ways that bars can lose their straightness.

Six Ways Bar Straightness Can Be Degraded

1) Mechanical damage to an end.   If the bundle is struck by a lift truck, or if the bars catch on a rack or table while being hoisted with the crane, this can cause the ends of the bars that are caught to be deflected out of the bundle and bent.

2) Improper blocking and support at mill or on truck. Cold finished barstock, especially smaller diameters, really needs to be supported at multiple points along its length. This reduces the possible radius that the bundle can sag or droop between supports. The mills that I’m familiar with, (PMPA Tech members) are pro’s and know the best way to support the product and to package it securely. Reputable mills put more bands on smaller ID bar bundles to preserve straightness when needed.

3) Truck loading  and securing. The binders used to secure the bars onto the truck can cause a permanent deformation if they are not matched up with the blocking beneath the bars. I saw a trucker once use a 4 foot piece of pipe as a “cheater” to secure the binding chains ‘one more notch.’ You could hear the wood  underneath the bundle being crushed. Chains are always bad news for cold drawn bars- nicks, and gouges and ‘low spots.’

4) Improper unloading. Putting a spreader bar on so that there are multiple points of support for the bundle is critical, especially with the smaller diameter bars and small bundles.

This is bad...

This is bad...

 I have seen shops unload bundles by using a single “hitch” at the approximate middle of the bundles. This causes a permanent camber over the length of the bars. Jerky crane lifts rather than smooth movements can magnify this effect.

5) Hand unloading or using a forklift. Small diameter bars especially can be bent by the way they are manually pulled out, lifted, and carried, instead of being placed on a table or rack. Using a forklift can also cause bars to be bent.

6) Frequency of handling. If you are buying from a service center, the number of times that the material has been handled can double or triple,  compared to a direct shipment from the mill. Given that you may be buying non-bundle quantities, it is a fact of life that the number of lifts and handling increases dramatically with the additional destination of the service center, as well as in the act of splitting the bundle. 

When you encounter bar straightness issues, characterizing the way the bar deviates from straightness can help you determine which of the above factors might be the cause.

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