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Using machine-ready blanks (e.g., blanks that have been cut and precision ground on all six sides) eliminates the need to adjust setups and fixture offsets for each blank. In turn, this minimizes variation from part-to-part and increases part-to-part repeatability. Since the cost of machine-ready blanks is more than offset by labor and machine time savings, machine-ready blanks always reduce the overall cost of parts.
Benefits of Machine-Ready Blanks
Typically, mold manufacturers begin with raw stock sawed to rough dimensions. Before it can be finish machined into a mold component or a mold base, it should be machined to exacting tolerances on six sides. Often to reduce cycle time and cost, manufacturers machine the top and bottom only. Later in the process, this causes additional non-productive time, such as resetting fixture offsets, tool changes and part handling time.
A mold plate made from steel machine-ready blank can be premachined with holes and slots before sent to customer to further reduce finish-machining time. Photos courtesy of TCI Precision Metals.
When purchasing a machine-ready blank, it should come to your shop at specified net, close tolerances—ready to load, lock and go. Machine-ready blanks need no further prep and very minimal setup time before beginning value-added finish machining. The time and cost that are saved can be up to 30 percent or more.
Many manufacturers do not want to pay the additional cost for a machine-ready blank, instead preferring to purchase raw stock, saw it and rough machine it in-house. Because in-house blanks are generally not as consistent part-to-part as machine-ready blanks, they result in additional time spent on resetting fixture offsets, additional part handling and tool changes. All of this time ends up costing the manufacturer substantially more, as much and sometimes more than 30 percent of the completed component cost. Plus machines are tied up performing non value-added operations, when they could be making more components and molds.
The reason making machine-ready blanks in-house takes so much time and costs more is because they require specialized equipment and processes (see Specialized Equipment for Machine-Ready Blanks sidebar below), which cannot be justified. Tolerances of some machine-ready blanks can be as close as ±.0005" dimensionally and ±.0002" flatness, squareness and parallelism. The specialized equipment includes double-disc grinders, Blanchard grinders and duplex milling machines.
Example
Just one of many benchmarks demonstrating the cost savings that can be achieved by using the right machine-ready blanks involves a part made out of aluminum.
| Rough-Blank |
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Mold plates being milled with a duplex milling machine using opposing cutters that run the length of the material, remove equal amounts of material from each side simultaneously reduce cycle time almost by half.
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| Material: |
3/4 X 9 7/8 X 16 3/8 (Oversize)
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| Quantity: |
100 pcs |
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| Prep Machining: |
11.12 min |
| Operator Intervention |
15 min |
| (such as changing clamping) |
Finish Machining:
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54.83 min |
| Total Run Time: |
81 min |
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Machine-Ready Blank
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Material:
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.625 X 9.700 X 16.250
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Tolerances:
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+/-.001" Thickness, +/-.002" W/L
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Flatness:
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within .002" |
| Quantity: |
100 pcs |
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Machine-ready blanks are delivered ready to load, lock, and go. No further premachining or additional prep time required, saving as much as 30 percent or more of the net part cost.
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| Prep Machining: |
0 min |
| Operator Intervention: |
0 min |
(such as changing clamping) |
Finish Machining:
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54.83 min |
| Total Run Time: |
54.83 min |
| |
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Machining cost savings:
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$40 per part |
Material increase:
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$30 per part |
Total cost savings:
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$10 per part |
| Total job savings: |
$1,000 |
| Throughput increased: ≈26 minutes per part or 43.3 hours of machine time freed up for other jobs |
In the example, a machine-ready blank eliminated 11.12 minutes of time spent premachining a rough blank and 15 minutes of operator intervention time spent making five clamp changes. Machine-ready blanks saved $1,000 over the cost of the job—even though purchasing machine-ready blanks cost slightly more than beginning with raw stock. Plus the total amount of machining time saved by using machine-ready blanks in this application increased capacity by freeing up a week of production time on one machine for more jobs.
Summary
Ever since mold manufacturers awakened to find competition from places such as Canada, Eastern Europe, Mexico and China, they have sought technologies that would allow them to compete with cheap labor. Mold manufacturers are using lean practices and limiting bids to projects that match their special expertise. While technology has helped cut costs, there are many decades-old, low-tech solutions that can reduce high labor costs and increase productivity. Machine-ready blanks provide substantially reduced costs and increases in throughput.
Specialized Equipment for Machine-Ready Blanks
The equipment for producing machine-ready blanks efficiently may not be purchased off-the-shelf, including specialized Blanchard grinders, double-disc grinders and duplex mills. The machines of your machine-ready blank supplier should be retrofitted with CNC controls to improve accuracy and ensure repeatability; and their processes in place should be certified by ISO 9001:2000.
Blanchard Grinding, technically referred to as rotary surface grinding, quickly removes stock from one side of a part that is too large to be double-disc ground. Using significantly greater horsepower than other grinding methods allows Blanchard grinding to remove large amounts of stock quickly and efficiently. Ideal for large parts, such as rotary tables, mold plates, die sets and vacuum chambers, Blanchard grinding allows size versatility, eliminates mismatches and compared to flycutting speeds turnaround time on large parts. Moreover, Blanchard grinding is faster and less expensive than surface grinding.
Double-Disc Grinding is a highly efficient grinding method that uses two opposing abrasive wheels to simultaneously grind two sides of a blank at the same time. In one operation, equal amounts of material are removed from both sides. By automating double-disc grinding (high volume grinding) operations, cost-effective thickness sizing of typical mold components and smaller parts such as fine blanked, stamped, die cast, and sintered metal parts can be provided. Automation significantly reduces the production costs of large quantity runs.
Another benefit includes reducing internal stress in many materials. Simultaneously removing equal amounts of stock from two sides of a blank reduces residual stress. Less residual stress improves part stability during secondary operations and final machining.
Duplex Milling is the most cost-effective way to produce high quality, square-corner blanks. Blanks ready for duplex milling are clamped in place with two sides exposed for milling. Then, opposing cutters run the length of the material, removing equal amounts of material from each side. Milling two sides of the blank simultaneously reduces costs dramatically.
Furthermore, multiple blanks can be stacked and duplex milled, producing additional cost reductions and reducing turnaround time. Duplex-milled machine-ready blanks allow manufacturers to maintain high quality machining standards without wasting time and money squaring-up blanks in-house. |
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MACHINING
