Design Process: Special purpose machine

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Every engineering project is different, but this post describes a typical design process for a small special purpose machine.

Design Process Stage 1 – Initial concept modelling

Parts will be individually modelled in the CAD software based upon the machine’s overall requirements and geometry supplied from previous existing machines. Where dimensions are not available, representative geometry will be created based on photos and engineering good practice.

Individual parts look like this in SolidWorks:
Design Process: Individual Parts
The parts are ‘assembled’ within the CAD software in a way which reflects the actual assembly. In the case of a moving mechanism, a machine that moves in a particular way in real life will be able to move in the same way within the CAD model.

This is an assembly model in SolidWorks:

Design Process: Initial Assembly

In addition to presenting at a design review meeting, the initial concept model can be supplied as an eDrawing, allowing evaluation of a number of things. The model will be representative of the original design intent, but will not contain enough detail for full manufacture of the machine.

(eDrawings Viewer is a free cad file viewing package from SolidWorks which can run on Windows, Macs, iPad/iPhone and Android. edrawingsviewer.com)

The concept model evaluation may include:
– Function/operation and ergonomic considerations
– Budget costing for manufacture
– Starting the Design Risk Assessment process
– Initial evaluation against standards and regulations

The goal at this stage would be to agree the design with stakeholders in terms of operation, overall sizes, and performance specification.

Design Process Stage 2 – Proof of design

General engineering experience and the Risk Assessment will highlight parts/subassemblies which need validation for strength. After determination of the forces, SolidWorks Simulation will be used to analyse the imposed stresses in these parts. This information will be used for material selection and (potentially) determination of non-destructive testing requirements. The calculations will be kept and will form part of the Technical Dossier for the machine’s certification.

This is a stress analysis in SolidWorks Simulation:

Design Process: Stress Analysis

Design Process Stage 3 – Final design and detailing

Model refinement

The overall model will be refined to a suitable level which allows manufacturing drawings to be created from it. Final specs will be defined for third party items such as motor and bearings.

Drawing creation

The 2d drawings are created from the 3d part/assembly models, so all data is associative. (ie a change to the model updates the geometry shown on the drawing). Drawings will be supplied in PDF format. Where required, cad models can be sent direct to suppliers (for example cad files of sheet metal blank developments can be emailed directly to the laser cutters).

As with the proof of design, the drawing pack will form part of the Technical Dossier. At project completion all cad files/data/documents will be supplied to the client, to keep for any potential future use.

Design Process Stage 4 – Other Optional Activities

– Assistance with commissioning documentation (ie test protocols for the machine prior to putting into service).
– The SolidWorks model of the machine may be used to create imagery for the machine’s Operation and Maintenance Manual.
– Creation of rendered images for marketing purposes, as shown below.
Design Process - Rendered Image