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EPT 221ENGINEERING DESIGN

Defining and Solving Design Problems

Objectives of this Lecture

• To describe different types of design problems

• To define and describe the different types of designs

• To describe and identify product and process plant components.

• To identify (decompose and diagram) a product’s components.

Different Types of Design Problems

• A design problem can be either:– design improvements improvements to existing products– developing a new product

• A design problem can be defined as a product deficiency that needs resolution, or a product opportunity that needs consideration.

• A design problem can also be either:– A one-piece product – shaped from a single material.

E.g. toothpick/ baseball bat.– Complex products - include thousands of components made with different

materials or manufacturing process. E.g. commercial jet airplane, automobile.of different materials and manufacturing processes.

• Customers and consumers.• Technology readiness.• Quantities of production:

– Mass production e.g. toothpick– One-of-a kind e.g. potato-chip packaging machine

Example of Products

• Are all these products the same?

Product Anatomy

• Product : – an item that is purchased and used as a unit (Dixon and Poli,

1995).– complexity of a product depends on:

numbers type function

of their components so, the less the number of components, the simpler the product.e.g. of single-component products paper clip, canoe paddle, toothpick. e.g. complex products penlight, bicycle, toaster oven.e.g. very complex products refrigerator, automobile, commercial jet airplanes.

– composed of components that include parts and assemblies.

Parts and Assemblies

• Parts : a single piece requiring no assembly sometimes called piece-part.• Assembly : a collection of 2 or more parts or subassemblies. • Sub-assembly : an assembly that is incorporated into another assembly or

subassembly. • Standard part : a common interchangeable item, having standard features, typically

mass-produced, used in various applications. E.g. screw, bolts, nut, washer, etc.

• Special-purpose part: a part designed and manufactured for a specific custom application.E.g. support bracket, engine housing, etc.

• Standard assembly/ subassembly: one that is commonly sold and used in various applications.E.g. pumps, electric motors, HE, small gasoline engines.Sometimes called modules.OEM (Original Equipment Manufacture): companies that use standard components purchased from one or more suppliers.

• Special-purpose assembly: an assembly that is designed for a specific application.E.g. a garden tractor transmission, etc.

Example: Penlight assembly drawing

Special-purpose part

Special-purpose part

Standard part

Special purposepart – to hold the

bulb

Sub-assembly-composed of glass lens,filament, base- also a standard sub-assembly-mass-produce and made in standard sizes.

Standard sub-assembly-anode, cathode, electrolyte paste, plastic cover

Product-component Decomposition

• The process of categorising the components of a product into parts and assemblies product-component decomposition.

• The diagram illustrates the basic structure of the components/ product anatomy.

• The diagram assists the development team in exploring the relationships between components types and functional performance.

• Useful during reverse engineering.

Example: Product Decomposition Diagram of a Penlight

• The penlight is an assembly of 2 subassemblies (bulb and battery) and 4 parts (case, cap, spring, button).

• Bulb: function to convert electricity to light• Battery: function to store electrical energy• Case: function to support the components as well as conduct

electricity from the battery to the bulb.• The decomposition diagram shows that the penlight assembly

depends upon • selecting and purchasing standard components (bulb, spring,

battery).• Design and fabrication of the special-purpose parts (cap, button,

case) decisions to be made regarding the appropriate material and manufacturing process for each part.

Exercise

• Prepare a product component decomposition diagram of an electric space heater. The heater has: (1) a special-purpose metal enclosure subassembly composed of a housing and an open-faced grill,(2) a standard blower subassembly composed of a fan and electric motor,(3) an electric special purpose module subassembly of a blower switch, heater switch, safety tip-over switch, and a power cord,(4) a special-purpose heating element, which uses nickel cadmium wire wrapped around a ceramic frame, (5) and six machine screws that fasten the subassemblies.

Process Plant Anatomy

• A process plant is a combination of systems used to process energy or materials (both organic and inorganic).

• A one-of-a-kind design: customized to meet specific needs.• E.g. meat and vegetable processing iron ore processing, petroleum

plants, stamping plants, hydroelectric power plants, steel plants.

• System: 2 or more pieces of equipment used to perform a set of process.

• E.g. waste treatment, auxiliary power generation, materials handling, HVAC.

• Equipment: machines/ apparatus designed to perform simpler specialized processes.

• E.g. feed water pumps, boilers, condensers, electroplating tanks, paint sprayers.

• Process: mechanically, chemically treat matter so as to change its properties.

• E.g. refrigerating, heating, separating, distilling, refining, spraying, chilling, evaporating, melting, homogenizing, freezing, heat-treating, cleaning, inspecting, sorting.

• So, process plant is an integrated arrangement of systems, and pieces of equipment.

• 4 systems: washing, blanching, freezing, packaging.

• Process???

Types of Design1. Variant Design

Modifying the performance of an existing product by varying some of its design variable values or product parameters such as size, or specific material, or manufacturing process (Pahl and Beitz, 1996) while maintaining the fundamentals working principles or concept.E.g.: (i) modifying the length of a lever to increase mechanical advantage, or aluminum for a

part rather than steel to reduce weight, or (ii) using die casting rather than sand casting to reduce processing costs.

2. Adaptive DesignAdapting a known solution to accomplish a new task (Pahl and Beitz, 1996).E.g. adapting the ink-jet printer concept to spray a glue to bind powders in layers as a rapid prototyping methodadapting the cell phone concept to include personal digital assistant functions

3. Original Design

- conceiving and embodying an original innovative concept for a given task (Pahl and Beitz, 1996). - the development of a new component, assembly, or process that had not existed before (Ulman 1997).

4. Selection design – matching the desired functional requirements of a component with the actual performance of standard components listed in vendors catalogue. E.g. to design a belt-and-pulley drive, need to determine the belt type and size to design a new lawn tractor, need to select the size and type of gasoline and type of wheels.

5. Part, Assembly, Product Design- the different degrees of complexity.

6. Concept Design, Configuration Design, Detail Design- refers to the phases in the engineering design process- E.g. concept design alternative working principles (an electric motor, steam engines, gasoline engines?)- configuration design determine the number, type and approximate arrangement of geometric features.

7. Redesign:– improving an aspect of form shapes, sizes, configurations, materials, manufacturing

processes. 8. Artistic design:

– deals with an object’s appearance– not engineering design does not apply science and mathematics to predict the

behaviour of a candidate design before it is made.9. Tinkering:

– How design are made early in history.– not engineering design product which has not been engineered. – E.g. pots, pans, cutlery, chairs, sofa, beds.