Part Cost Estimator: Assumptions and calculations

Assumptions used by the model

The following assumptions are made by the Part Cost Estimator:

• All material and process combinations are viable (i.e. no validation is carried out).
• The overhead rate and capital write-off time for the primary and secondary process are the same.
• The material utilization factor for the primary process is the maximum value quoted on process datasheet (i.e. process has been optimized to minimize scrap levels).
• All waste material from the primary process is recycled (only if recycling is permitted by the choice of material).

Assumptions on material price

Material price depends on many factors including availability, volume purchased, price volatility of the feedstocks that are used to make it, and manufacturer's certifications that it carries. The material price quoted on the MaterialUniverse datasheet is an approximate price for high volume purchase from a primary producer.

With the exception of ceramics, metal matrix composites, and foams/honeycombs, the quoted price is that of the material precursors used in the shaping or forming process. For example, the price quoted for 'Aluminum, 7075, wrought, T6' represents the price of billet used at the start of the manufacturing process and does not include the price of rolling or heat treatment.

It is therefore important to add the processing of these material precursors as the primary shaping process, if you are using one of these materials in the Part Cost Estimator.

The material form represented in the material price is summarized below for each material family:

Material category	Material Form specified in MaterialUniverse price value
Metals - wrought	Billets/ingots/cathodes
Metals - cast	Remelt ingots/scrap
Thermoplastics and TPEs (injection and extrusion)	Resin granules/pellets
Thermoset plastics	Resin, fillers, and additives
Rubbers (thermoset elastomers)	Unvulcanized gum, fillers, and additives
Polymers - composites	Resin and reinforcement/prepregs
Ceramics and glasses	Simple molded/sintered parts
Foams and honeycombs	Foam or honeycomb sheet
Natural materials - fibers	Untreated fiber
Natural materials - minerals	Undressed block, powder
Natural materials - woods	Merchant wood (dried and cut)

Calculations used by the model

The full part cost, C, is divided into three separate components:

where C_pp = cost of material and primary processing, C_sp = cost of secondary processing, and C_rc = credit received for recycling waste material. For a full list of symbols, see list of symbols used in part cost estimator.

Primary process cost (C_pp)

where m=component mass, C_m=material price per unit mass,  f_pp=material utilization factor (primary process), f_sp=material utilization factor (secondary process), C_t=tooling cost, n=batch size, n_t=tool life, C_oh=overhead rate, =production rate, C_c=capital cost of equipment, L=load factor, t_wo=capital write-off time.

The first term on the right represents the total material price, the second term is the tooling costs, and the third term is the overhead costs (from the capital overhead, labor costs, and production rate).

For continuous (rather than batch) processing methods, replace with and replace n_t with n_t /l.

f_pp and f_sp are the material utilization factors for the primary and secondary processes. These account for the waste produced by both process steps, and convert the specified component mass into the initial mass of material that is fed into the primary process. If there is no secondary process, then f_sp=1.

C_oh/(C_ohUSA) is a correction factor for the tool cost that accounts for differences in the overhead rate between countries. The base values stored in the database are from the USA.

Secondary process cost (C_sp)

The secondary process cost equation takes a similar form to that of the primary process cost equation, but without the factor for material price.

C_t, C_c, n_t, and t_wo in this equation represent values for the secondary shaping process.

Credit for recycling (C_rc)

If the material can be recycled (stated on material datasheet) and Scrap recycled? under secondary process is set to Yes, then credit is obtained for recycling. The credit is offset against the manufacturing cost of the component. All scrap material from the primary process is assumed to be recycled where possible.

Part size and complexity

The size and complexity of a part has a large effect on capital cost, tooling cost, tool life, and production rates. As the part becomes larger and more complex:

• Capital cost increases: large machines are required to fabricate large components.
• Tool cost increases: large tools are complex and need to resist high operating temperatures and pressures.
• Tool life decreases: high temperature and pressure increases the strain and wear on processing tools, decreasing their lifetime.
• Production rate decreases: large part sizes take longer to process, complex parts require precision processing.

The part size and complexity are ranked using a simple three-point scale. The characteristics above are evaluated and included in the part cost calculation by estimating the correct portion of the value range to be applied, based on the part size and complexity ranking. The table below shows the value range for the tooling cost (C_t), using the range quoted on the ProcessUniverse datasheet, and the specified part size and complexity:

Tooling cost (portion of value range used)		Part complexity
		Simple	Standard	Complex
Part size	Small	low	low-mean	mean
	Medium	low-mean	mean	high-mean
	Large	mean	high-mean	high

For example, for a standard part complexity and large part size, the tooling cost would be in the mean-high end of the range.

In practice, the Part Cost Estimator calculates the part size by comparing the component mass (m) with the mass range quoted on the ProcessUniverse datasheet for the selected processing stage, and determines the part size based on where it lies on the quoted range. This value is then combined with the part complexity value to determine the value of the capital cost (C_c), tool cost (C_t), tool life (n_t) and Production rate () to use.

Machining processes

Machining processes are different to other processing methods, and so a modified calculation is used when using these processes in the part cost estimator.

Machining process costs are determined by the amount of material removed (rather than part size or complexity), and the relative machinability of a material (for example, aluminum is easier to machine than steel, which is easier to machine than titanium).

The machining process calculation uses the Amount of scrap value entered by the user to calculate the amount of material removed, and uses the Machining speed quoted on the MaterialUniverse datasheet to calculate the machinability of the selected material. If no machining speed is quoted on the datasheet, then a value is estimated from the material's Hardness and Young's modulus.

Table of overhead rates

All figures quoted are in USD/hour. Overhead rate includes the local labor rate and the overhead for running the processing facilities, based on labor and energy rates in the different countries and regions.

Region / Country	Overhead rate (USD/hr)
World	60
Europe	131
Former USSR	22
North America	117
South America	62
Asia	52
Oceania	147
Middle East	53
Australia	190
Austria	179
Belgium	201
Brazil	70
Canada	122
China	22
Czech Republic	90
Denmark	182
Finland	164
France	161
Germany	191
Greece	108
Hungary	76
Iceland	149
India	23
Ireland	171
Italy	167
Japan	177
South Korea	82
Mexico	62
Netherlands	160
New Zealand	109
Norway	208
Poland	66
Portugal	91
Russia	22
Slovakia	98
South Africa	33
Spain	126
Sweden	180
Switzerland	216
Turkey	72
United Kingdom	143
United States	150