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Unit Cost Models for Product Design (TF vs. IM) What we are going to do. Why we are doing it. How we are going to do it. TEC 315 Dr. Lou Reifschneider. WHAT we are going to do:. Compare Costs of Competing Manufacturing Processes
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Unit Cost Models for Product Design(TF vs. IM)What we are going to do.Why we are doing it.How we are going to do it. TEC 315 Dr. Lou Reifschneider
WHAT we are going to do: Compare Costs of Competing Manufacturing Processes • Compute the unit cost (break even cost) to make a product via thermoforming, • Compare this unit cost to the unit cost if made by Injection Molding.
WHY we are doing this: • A major responsibility of the product designer is to determine the most economically competitive method of production. • Detailed product design will depend upon the process chosen for manufacture.
How we are going to do it… • Overview of the major cost inputs to make parts by either Thermoforming or Injection Molding. • In-class practice to estimate the Unit Cost of a simple product using the two methods. • Homework for next week is to bring completed analysis of another product. • You will determine a unit cost for your own design product.
Unit Cost Model Focus: 4 inputs plus 2 additional for TF • 1) Tooling cost per unit • 2) Material per unit • 3) Labor Cost per unit • 4) Machine Cost per unit Additional charges if thermoforming part: • 5) Trimming Fixture • 6) Trimming Labor
Fixed Costs and Variable Costs • Fixed Costs – cost is independent of number of parts being made, for example: • Tooling (per order size), • Fixtures (for trimming per order size). • Variable Cost – incur cost with each product made, e.g.: • Material (sheet stock TF, resin shot size IM), • Labor (and/or machine rate) for primary processing, • Labor (and/or machine rate) for trimming (TF).
Unit Cost relationship to Order Size • NOT sensitive to cost of material or processing. • IS SENSITIVE to tooling (fixtures, programming, set-up), • MUST KNOW ORDER SIZE to compute the unit cost of the FIXED cost inputs. Fixed Cost / Order Size Baseline Unit Cost = material and processing Unchanging w/ Order Size
Unit Costs: 4 main drivers • Mold Tooling cost per unit = • Mold cost / parts made per mold (order size) • Material cost per unit = • IM: Part weight x material cost/lb • TF: blank size x material cost/SF (web included in bulk part size.) • Processing cost per unit = Labor + Machine • (Labor rate)/hr x hours per unit • (Machine rate)/hr x hours per unit • (Need cycle time for this calculation).
Unit Costs: additional costs for TF • Trimming Tooling cost per unit = • Equipment cost / parts made per tool (order size) • Trimming labor cost per unit = • (Labor rate)/hr x hours per unit • (Need trimming time for this calculation).
HDPE(sec) = 600 x thickness (in) ABS(sec) = 325 x thickness (in)
Economics of TF and IM (1/3) • Tooling cost – consult instructor • Order size – consult instructor • Material Cost per part (material cost table) • TF: $/SF x SF/part (note need web for clamping) • IM: shot size (lb/part) = in^3/part x lb/in^3 • Part volume from Analysis/Measure Bodies/… • IM: $/lb x shot size • Cycle Time per part (cycle time table) • TF(sec): 20 + Material Factor x Thickness (in) • IM(sec) 5 + Material Factor x Thickness^2
To determine the volume of a molded part: Analysis/Measure Bodies/… Volume is first option on pull down menu.
Economics of TF and IM (2/3) • Production Hours • Production Hours = sec/part x parts/order / [3600 sec/hr] • Labor Rate – labor cost table • Machine Rate – machine cost table • TF: $30/hr • IM: [30 + 0.06 x Tons] ($/hr) • Tons = 3 x projected area (in^2) (from CAD) • Labor & Machine Costs • Rate x Production Hours
Economics of TF and IM (3/3) • Thermoforming additional • Trimming Fixture – consult instructor • Trimming Labor Cost = Labor Rate ($/hr) x Trim Time/part (sec/part) / [3600 sec/hr] • UNIT COST = Total Costs / Order Size ($/part)
In-Class Example (1/2): Pad Locator • Assume 10,000 unit volume run. • Part specifications relevant to cost analysis • made of ABS; • nominal thickness = 0.125”; • 8” x 8” in size, 1 inch high with 2” hole in center. • Thermoforming: • Need 10” x 10” x .125” sheet. • Will need to trim perimeter and hole. • Injection Molding: • Part volume = 11.14 in^3 (Analysis/Measure Bodies/..) • Part projected area = 64 in^4 (8x8 approx.)
In-Class Example (2/2): Pad Locator • Refer to Summary Section of Unit_Cost template. • Change the order size with all other parameters fixed. • Generate a table of unit cost per order size for each process. • Graph using table like shown. • Note when unit cost lines cross: switch-over point to use one process vs. the other.
Class Practice: Hypothetical Part • Projected area: 400 in^2 (2.77 SF) • Thickness = 0.125”, ABS material • Part volume = 50 in^3 • Need 10,000 per year (start calculations). • TF mold cost = $4,000, Trim Fixture = $500 • Trimming time/part = 60 sec. • IM mold cost = $40,000 • Labor rates = $15/hr. • Machine rates per Machine Cost Table.
