Cycle Time First, Tooling Second

Cycle Time First, Tooling Second

Shops Should Not Base Tooling Decisions on Price Alone.

ADVANCE MACHINING & GEAR CUTS machining cycle times first. Then it looks at reducing its tooling costs. As far as the shop is concerned, cycle times play the key role in maintaining competitiveness, and by making cycle times as short as possible, it delivers jobs faster and handles more work, and doesn't have to invest in new equipment to do it. The shop also can quote jobs more effectively to protect its margins, especially for long-run, repeat work that it wins by providing quick job turnarounds and by meeting customers' just-in-time delivery requirements.

"These days, customers of job shops are increasingly willing to pay a premium for reliable, quick deliveries," says Tom Craze of Ingersoll Cutting Tools (www.ingersoll-imc.com). "So, cutting cycle time becomes way more important than reducing tooling costs, which typically represent less than 10 percent of part cost anyway."

However, the opposite often happens. Shops frequently focus too much on the price of tooling and tool-life-for-thedollar, in effect, turning tooling into commodity items based on the assumption that tools that look alike, perform alike. When, in reality, one tool could do the job in half the time the other does.

Craze worked with Advance Machining & Gear's Kyle Dunaway in a plant-wide retooling project to support the Grove City, Ohio, shop's expansion into new markets. The retooling saved Advance Machining & Gear more than $100,000 a year in milling, turning and holemaking costs. As a result, Advance Machining & Gear has tripled its number of CNC machines, from five to 15, and has picked up more long-run business.

One of the shop's first jobs after the retooling was for wedges that were machined from lengths of mild, 1018 steel bar stock. The initial order was for 1,200 pieces and a promise of repeat orders. So, spending a little more on tooling to reduce cycle times made sense.

Advance Machining & Gear ran eight wedges at a time on a 4-axis Matsuura horizontal CNC mill using a 2-in., zero-rake milling cutter. The shop used a solid-cobalt twist drill for holemaking. Cycle time to mill and drill each batch was 182 min running the milling cutter at 700 rpm and feeding at 40 ipm. After retooling with an Ingersoll 1-in. IC Form-Master button cutter and replaceable-tip Qwik-Twist drill, the shop slashed cycle time to less than 79 min. That is less than half the previous cycle, and it saved more than $10 per part. The shop cut $15,000 in costs from the job that is now repeating at 600 pieces per month.

The majority of Advance Machining & Gear's chipmaking involves rough milling steel and cast iron. Dunaway says the company saves the most — $75,000 per year — by cutting cycle times for these operations. The shop has standardized its milling operations to run at 100 ipm and 1,500 sfm and, depending on workpiece and cut geometries, it uses either an Ingersoll V Max, Form-Master or Hi Pos milling cutter, all of which remove material twice as fast as any cutters the shop previously ran.

According to Ingersoll, running faster at the expense of tool life saves more than running at slower speeds to try to extend tool life. Here's why: Machine and labor time represents about 40 percent of the cost of a machined part, while tooling typically represents about 3 percent of the cost. Based on that, a shop that cuts cycle time by 30 percent, reduces total part cost 12 percent (0.30 0.40 = 0.12). For comparison, if the same shop extends tool life by 20 percent, it may reduce its tooling cost by 16 percent (0.20/1.20 = 0.16), but it only reduces part cost by 4.8 percent (0.3 0.16 = 0.048).

THE CYCLE TIMES KEEP DROPPING
The cost of tooling is negligible when a shop can double or triple its productivity for an operation by reducing cycle times, says William Greenleaf of Greenleaf Corp. (www.greenleafcorporation.com). To illustrate this, the cutting tool company provides a tool-justification worksheet (above) developed from a recent customer application.

The worksheet points out that the cost of using the insert that is initially more expensive is lower than the cost of using the other tool. On a cost-per-insert basis, the first tool costs four times as much as the other. When looked at in terms of cost of cut per part (insert + machine time), the tool that is initially more expensive costs 56 percent less than the other tool.

WHAT'S THE PAYBACK?
Michael Gugger, manager of special projects at TechSolve Inc.(www.techsolve.org), says shops should focus less on a new cutting tool's cost and more on when and if it pays back. TechSolve is a consulting firm that specializes in helping manufacturers to implement process changes that boost productivity.

Gugger warns that shops first and foremost must have machine tools that have the power and capability to handle the process parameters provided by advanced cutting tools. If a shop does not have those machine tools, then its payback comes only from tool life.

Gugger also says the key to success for most shops is a willingness to risk change, and investing time and money to increase productivity. He gives the example of an aerospace supplier that sharply reduced its machining cycle time for a troublesome titanium part.

Process time was more than 20 hours per part, and material costs were high because the shop used excess material to dissipate heat generated during machining and to reduce warping. TechSolve tested a variety of machining conditions at its machining laboratory and at the shop and determined that changing tooling would help the shop to develop a best practice to machine the titanium part.

TechSolve recommend that the shop use a 10-flute, TiAlON coated, solid-carbide end mill that cost about 40 percent more than the tool the shop was using. The consulting firm also recommended that the shop use high-pressure coolant and five-axis machining. The multi-axis machine tool would tilt the cutting tool slightly — about 1 degree off vertical — into the material to optimize machining.

The ten flutes on the solid-carbide tool reduced chip load per tooth and let the shop increase its feedrate per revolution. This simultaneously reduced cutting forces, boosted metal-removal rates and generated less heat. Also, the highpressure coolant provided additional cooling by forcing the metalworking fluid into the cut zone. Meanwhile, tilting the tool by one-degree off vertical provided greater access for the coolant to wash over the part while it disengaged the tool's cutting edges from the cut. That single degree of detachment from the cut also increased the cooling process.

The shop slashed the titanium part's original cycle time by one-half as a result of incorporating these changes. Also, the more effective thermal-management techniques allowed the shop to reduce material requirements by one-third because it eliminated the extra stock it had engineered into the workpieces to improve cooling, to guard against warping and for "sneaking up" on finished geometries.

According to Gugger, too many shops, especially those that are purchase-driven, consider only the cost differential when making a tooling decision and seldom evaluate actual savings and payback (see Five Steps To Tool Payback below).

Comparison of inserts for rough turning turbine discs
Greenleaf tool(VCGN-2.532V WG-300) Current tool (VNMG-432)

Price per insert

$26.59 $6.00
Speed 1,200 sfm 110 sfm
Feed 0.004 ipr 0.007 ipr
Depth of cut 0.03 in. 0.03 in.

Number of edges per insert

2 4

A. Number of cuts (or parts) per edge

0.50 0.25
B. Insert cost per edge $13.30 $1.50
C. Insert cost per cut (or part) B/A $26.59 $6.00
D. Cycle time per cut (or part) 2.34 min 38 min
E. Machine cost per hour $100 $100
F. Machine cost per cut (or part) $3.90 $63.33
Total cost cut/part (insert + machine time) $30.49 $69.33
Parts/cuts per shift, job, year, etc. 1,500 1,500
Total cost savings (shift, job, year, etc.) $58,265

FIVE STEPS TO TOOL PAYBACK

TechSolve has a five-step process to determine the payback of using different tools or incorporating a new tool or another tooling system. In the first step, a shop identifies its goal or what it wants to compare. The second step is evaluating the current practice or the tool currently in use. The third step is evaluating the new practice or tool. The fourth step is to compare the current practice or tool to the new practice or tool.

The final step is to determine the payback, or the break-even point. That is the point in production at which the increased cost of a new practice or tool has been repaid by the savings. After that, a shop begins to profit from the new item. According to Gugger, a shop must reach this payback level of production, or the tool it is considering is not worth purchasing.

The following charts illustrate how these five steps can be used to justify new technology using a highspeed steel (HSS) drill as the "as is," and a coated high-speed steel (CHSS) drill as the "to be."

Machining cost: HSS drill
Tool cost ($/life) Machine burden ($/min)
A. purchase price $3.50 G. hourly rate $30.00
B. cost per regrind $1.50 H. minutes per hour 60
C. regrinds 3 I. machine burden (G / H) $0.50
D. regrind cost (B x C) $4.50
E. lives/edges (C + 1) 4
F. cost per life ((A + D) / E) $2.00
Total tool cost (A + D) $9.00

Machining cost: coated HSS drill
Tool cost ($/life) Machine burden ($/min)
A. purchase price $5.00 G. hourly rate $30.00
B. cost per regrind $2.00 H. minutes per hour 60
C. regrinds 2 I. machine burden (G / H) $0.50
D. regrind cost (B x C) $4.00
E. lives/edges (C + 1) 3
F. cost per life ((A + D) / E) $3.00
Total tool cost (A + D) $9.00

Five Steps to Justify New Technology
Step 1: Cost per hole
Step 2: HSS drill (as is) Step 3: CHSS drill (to be)
Productivity: 8.8 holes/min Productivity: 14.9 holes/min
Tool life: 16.3 min Tool life: 9.05 min
Cost: $0.62/min (to operate the tool) and $0.071/hole Cost: $0.83/min (to operate the tool) and $0.055/hole
Step 4: $0.071 – $0.055 = $0.016/hole savings
Step 5: $9.00 (CHSS total tool cost) – $8.00 (HSS total tool cost) / $0.016 (savings/hole) = 62.5 holes payback level
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