General Process
The following sections list Assembly processes, describe some important assumptions of the Assembly cost model, and discuss several ways in which Assembly processes differ from the processes in other process groups.
Supported Processes
Assembly process group routings support the following main processes:
• Pick and Place: includes picking each subcomponent from a bin and loading into the assembly or fixture. It also includes clamping the part in the fixture and/or reorienting the part if necessary.
• Lock Bolt: uses a bolt-type fastener which is permanently installed and cannot be removed, providing a vibration resistant and maintenance free joint. You must manually assign the Lock Bolt operation (Lock Bolt Install) to one member of each pair of subcomponents to by joined in this fashion.
• Threaded Insert: installs inserts into threaded holes in order to make screws and bolts more secure and resistant to vibrations and impacts. You must manually assign the Threaded Insert operation to one member of each pair of subcomponents to by joined with the help of such an insert. (You must separately assign a Screw Tighten operation from the Mechanical Assembly process.)
• Rivet: either rivets all holes within a specified size range, or rivets a specified number of holes.
• Mechanical Assembly: includes assembly operations that are assumed to be performed by hand on specified components. These operations include Nut Insert, Rivet, Press Fit, and Tab Bend, among others. You must manually assign an operation to each subcomponent that requires it. In a case where two subcomponents are held together with a fastener, a fastening operation only needs to be applied to one of the subcomponents.
• Adhesive Bonding: uses a high-strength bond to join components that are made of various materials. You must manually include the Adhesive Bonding process in your routing; adhesive bonding is then assumed to be applied to a certain percentage of the assembly's total surface area (10% by default, in starting point VPEs).
• Sealing: there are three sealing processes, which are used to prevent gas or moisture from getting between components:
o Cap Sealing: applied around fasteners or rivets.
o Fay Sealing: used to prevent galvanic (dissimilar metal) corrosion.
o Fillet Sealing: applied to relatively long, thin regions.
• Welding: there are eight welding processes:
o Manual MIG Welding
o Manual TIG Welding
o Manual Spot Welding
o Robotic MIG Welding
o Robotic TIG Welding
o Robotic Spot Welding
o Electron Beam Welding
o Laser Welding
Each welding process has a single operation, which the cost model applies to each appropriate Weld GCD—see Welding Operation Feasibility for more information.
Welding is optionally preceded by the Weld Prep process (Bevel Cutting, Grinding, and/or Wire Brushing operations) and optionally followed by Weld Clean Up (Grinding operations). You must manually assign the appropriate prep and cleanup operations to the appropriate Weld GCDs.
Optional secondary processes include Machining, Surface Treatment, Heat Treatment, and Packaging, if you have licensed these modules.
Assembly Cost Tables
The cost tables for assemblies include the following:
• Assembly Details
• Assembly Tracker
• Cost Summary
See Assembly Views for more information. See also the Cost Tables chapter of the aPriori User Guide.
The Cost Summary table for assemblies has several notable features:
• All costs listed at and above Assembly Process Fully Burdened Cost including only costs for assembly processes, and exclude costs for manufacturing the subcomponents.
• Subcomponent process costs are listed at Fully Burdened Cost of Subcomponents.
• Material Cost is always 0.
Labor Time and Cycle Time
The assembly cost model derives costs largely from data about standard times associated with basic assembly tasks (such as tightening a screw, or bending a tab). For each task, this is the time it takes one operator to perform that task. The model calculates labor time per part based on these values. In contrast to other process groups, which derive labor time from cycle time, Assembly processes derive cycle time from labor time.
Labor Time, Cycle Time, and Number of Operators
For processes from other groups, increasing the number of operators typically increases labor time and labor cost per part, and does not affect cycle time per part. For Assembly processes (except robotic processes), in contrast, increasing the number of operators decreases cycle time and does not affect labor time or labor cost. The Assembly cost model assumes the use of an assembly line that can be sped up or slowed down through the addition or removal of operators.
In general, with the exception of robotic processes, cycle time is assumed to be inversely proportional to the number of operators, and labor time is assumed to be independent of the number of operators—with certain exceptions related to robotic processes.
Overhead
As with other process groups, indirect overhead for Assembly processes depends on cycle time:
Indirect Overhead Cost per Part =
Indirect Overhead Rate * (Cycle Time + Amortized Batch Setup) / Final Yield
But unlike other process groups, direct overhead for Assembly processes is independent of cycle time:
Direct Overhead Cost per Part =
((Labor Cost * Overhead Multiplier) + (Direct Overhead Rate * Labor Time)) / Final Yield
Cycle Time Overrides and Adjustments
Because cycle time does not affect direct overhead, and because cycle time is derived from labor time (and not vice versa), cycle time affects costs only through its effect on indirect overhead. This means that overriding cycle time (or adjusting it with the cost model variable cycleTimeAdjustmentFactor) doesn’t affect labor time or labor cost. You should override or adjust cycle time only to affect indirect overhead, for example, to account for the cost of extra buffer space required by an unbalanced push assembly line.
Task Parallelism and Robotic Welding
For routings that include Robotic MIG Welding or Robotic TIG Welding, the cost model assumes that at least some of the Robotic Welding operators perform manual tack welding and pick and place tasks, in addition to tending to one or more robotic welding machines (one, by default). This can sometimes reduce costs compared to routings with Manual Welding, because the operator is assumed do tacking and pick and place on one piece during the time that the robot is welding another piece.
The number of operators for the Pick and Place process (specified by a PSO or machine property) indicates the total number of operators performing pick and place tasks, including the Robotic MIG Welding operators that perform pick and place tasks. By default, for routings with Robotic MIG Welding, the cost model assumes that there are no dedicated pick and place operators, and that all pick and place tasks are performed by one Robotic MIG Welding operator.