18 Scheduling Materials M aterials and parts are just as much part of the resources for projects as money and labour. Although the examples given in Chapters 16 and 17 demonstrated the scheduling of human resources, the same methods can be used for project materials. Most project management computer packages can carry out this function, provided that the materials requirements for any network task can be specified in amounts defined by simple units of quantity (for example, tonnes of sand). Project management packages can also be used to schedule the overall loading of manufacturing facilities.
But there are at least two aspects of project materials scheduling that need their own specialized procedures. These, which are outlined in this chapter, are the following: • scheduling parts and components for operations in manufacturing projects; • scheduling the purchases of equipment for capital projects such as mining, civil engineering, petrochemical projects and other large construction projects. MANUFACTURED PARTS AND MATERIALS SCHEDULING COMPARED WITH GENERAL PROJECT RESOURCE SCHEDULING Manufactured and purchased parts for manufacturing projects attract different scheduling problems from those associated with the purchase of bulk materials. A great deal more detail is required in manufacturing schedules than can easily or feasibly be included on the main project schedule.
Solving the problems of parts scheduling falls more properly within the ambit of operations management than project management (see, for example, Slack, Chambers and Johnston 2003). This chapter can, however, provide a glimpse into this subject. Parts scheduling requires close analysis of drawings, meticulous attention to detail, and specialized techniques. At one time the only practicable approach depended on manual methods, often using elaborate compilations of index cards.
The amount of work required could be prodigious, especially when attempting to identify and coordinate the usage of parts common to more than one part of the project or, worse still, common also to other projects and routine manufacturing. The methods were cumbersome, prone to error, and could not easily cope with changes. Those methods can be consigned to history and earlier editions of this book. Now the problems of complexity, inflexibility and errors can be solved more easily using computers.
Any system of parts scheduling demands the assembly of data structured on bills of materials or parts lists. Since these documents are products of design engineering, it follows that project parts scheduling cannot take place until design is substantially complete, considerably later in the project PROJECT MANAGEMENT life cycle than when the main project schedules are made. The methods described here assume that the project manager already has the main project plans and schedules, and knows when each significant assembly or subassembly will be required for the project. That information must be derived from the overall project plan (using critical path networks or bar charts).
Then, provided all the human resources and overall manufacturing facilities are scheduled sensibly (at departmental or group levels), production managers are given a time framework into which the manufacture and procurement of parts and smaller subassemblies can be fitted. Activities in overall project schedules cannot usually be chosen to show a depth of detail much smaller than main assemblies, or at least fairly large subassemblies. Factory schedules will even have to include all the separate manufacturing operations needed to make each part. Scheduling at the much greater level of detail needed for individual parts must be carried out by the manufacturing organization using their own specialized methods.
These manufacturing schedules might contain a mix of specially purchased components, items manufactured within the company’s own factory and other parts which are usually held in store as general stock. IDENTIFYING AND QUANTIFYING COMMON PARTS FOR MANUFACTURING PROJECTS The parts scheduling task is usually complicated because some of the parts for one assembly are also used on other assemblies or even other projects, so that provisioning must take all these different uses into account. Suppose that a project needs 100 cam-operated electrical switching subassemblies, all slightly different in design but each containing a particular type of microswitch in varying quantities. Thus there might be 100 sets of detail and assembly drawings for these switching subassemblies, each with its own parts list or bill of materials.
Someone has to discover how many of these switches are needed in total for the project, make sure that the requirements are collated, and that 100 separate purchase orders for microswitches are not placed. The same switching subassemblies might easily have other components that must be investigated to discover their total requirements as common items (cams and servo motors, for example). Batch differences Another complication arises if a project has to result in more than one similar output batch, produced at different times. Consider, for instance, a defence contractor who is working to produce a state-of-the-art weapons guidance system.
The initial contract might be for the design and manufacture of six identical Mark 1 prototype units, to be delivered at two-monthly intervals. An improved version (Mark 2) could be under development before all the prototypes have been delivered, so that Mark 1 and Mark 2 systems are both in different stages of production in the factory at the same time, with some parts common to both batches. While all this is going on, engineering changes can of course be expected to affect one or both batches, or even individual units within a batch. When parts scheduling becomes particularly complex, the project planner or project support office can provide help to the materials manager and production managers by collating all the known parts requirements, listing the assemblies and subassemblies on which the parts are to be used, and relating this information to the dates on the project plan.
That information can provide the input to a manufacturing requirements package (MRP II). 260 S C H E D U L I N G M AT E R I A L S CASE EXAMPLE: A FILING CABINET PROJECT Some aspects of parts scheduling for a manufacturing project can be demonstrated using a simple example. For clarity in these pages this study will not be taken down to the level of individual manufacturing operations and excludes finishing processes such as plating and painting. A company has designed a steel two-drawer filing cabinet, an exploded view of which is shown in Figure 18.
In the first instance, only one cabinet is to be made. Simple parts list for a filing cabinet All the parts needed for the filing cabinet can be seen in the exploded view (Figure 18.1), and these could easily be listed on a parts list or bill of materials. This might be compiled using a computer- aided design (CAD) system, or manually on a form such as that shown in Figure 18. The item numbers on this parts list correspond with those in the circles on the exploded view.
It shows total quantities without regard for breakdown into production subassemblies.1 Filing cabinet project: exploded view of the product 261 PROJECT MANAGEMENT Item Our part Description Quantity Remarks No. number Unit No 01 FC1001 Top panel Each 1 MF Panel shop 02 FC1002L Side panel, left Each 1 MF Panel shop 03 FC1002R Side panel, right Each 1 MF Panel shop 04 FC1003 Drawer chassis Each 2 MF Panel shop 06 FC1005 Rear panel Each 1 MF Panel shop 07 FC1006 Plinth Each 1 MF Panel shop 08 A502-A Runner, outer, left Each 2 SP Smiths plc 09 A502-B Runner, inner, left Each 2 SP Smiths plc 10 A503-A Runner, outer, right Each 2 SP Smiths plc 11 A503-B Runner, inner, right Each 2 SP Smiths plc 12 A209 Title card holder Each 2 CS Carter 13 A350 Handle Each 2 CS Epsom and Salt 14 S217 Screw Each 4 CS Acme Screws 15 W180 Washer,shakeproof Each 4 CS Acme Screws 16 S527 Screw, self tapping Each 12 CS Acme Screws 17 W180 Washer,shakeproof Each 12 CS Acme Screws MF = Make SP = Special purchase CS = Common stock Iss Mod No Date Iss Mod No Date Iss Mod No Date Iss Mod No Date A Prot 4Jun10 1 - 3Aug10 2 1 17Nov10 Drawn by: Checked by: Approved EFP TQM David Woodford Heath Robinson Furniture Plc Birmingham England Title: Filing cabinet: Elite series Sheet 1 Assembly number: Two drawer of FC 1000 Without locks 1 sheets Figure 18.2 Filing cabinet project: simple parts list 262 S C H E D U L I N G M AT E R I A L S Armed with the simple parts list, the company’s purchasing and production control departments would be able to provision all the materials by drawing available items from existing stocks, and either buying or making the remainder. There is no ambiguity about the total required quantity of any item and no complicated calculations are needed. Everything is detailed on one simple parts list.
Given a target completion date for the single cabinet, it would also be fairly simple to decide when each item must be ordered. Priorities must be given to those parts having the longest purchase or manufacturing lead times. Structured parts list for a filing cabinet The best sequence of manufacture for the filing cabinet would be as follows: 1. Make individual components and obtain bought-out items.
Assemble the parts into subassemblies. Carry out the final, main assembly. The simple parts list arrangement shown in Figure 18.2 is not very convenient for the production department because, ideally, they need a separate parts list from which to issue the manufacturing kit for each subassembly. In order to produce these separate parts lists, it is usual for the designer to start by drawing a family tree or goes-into chart showing how all the subassemblies and individual parts come together for the final assembly.
The family tree for the filing cabinet is shown in Figure 18. This is a hierarchical structure not unlike the larger-scale work breakdown structure for a project, but the level of detail here goes down to the very lowest level, including every nut, bolt and washer. Further, the tree must show the quantity of each part needed (the circled numbers in the figure show the quantities needed for each subassembly or main assembly on the next higher level of the tree). Coding (part numbering) is essential.
The example in Figure 18.3 reveals that four separate subassemblies have to be made before final assembly of one filing cabinet can take place. So, the simple parts list of Figure 18.2 has to be structured as five separate lists, one for each subassembly and one for the final main assembly. This arrangement is summarized in Figure 18. While the arrangement of parts lists in the filing cabinet family tree grouping (Figure 18.3) is ideal for manufacturing purposes, it is not so convenient for the purchasing of parts, or for the scheduling of manufacture for parts common to more than one subassembly.
For example, the washer, part number W180, is common to two assemblies. It appears twice on the simple parts list of Figure 18.2, where it is an easy matter to add up the quantities to find the total number of washers needed to make one filing cabinet (4 + 12 = 16). On the family tree in Figure 18.3 and on the manufacturing parts lists derived from it in Figure 18.4, this result is not quite so obvious. Anyone glancing at either the family tree or at the five separate parts lists might be forgiven for assuming that only 14 washers type W180 were needed (12 on the final assembly and two on the drawer assembly).
On each of the separate parts lists the washer (and every other item) only appears in the quantities needed to make one particular subassembly, regardless of how many subassemblies are needed. The catch is, of course, that two drawer assemblies are needed for one filing cabinet, so that the total number of washers needed for one cabinet is 12 + (2 x 2) = 16.
