The large financial outlay associated with production of HR moulds makes it advisable to perform a feasibility study (Figure 2.1) similar to that undergone when buying an injection moulding machine [1]. This gives the information necessary to decide whether it makes sense under the given circumstances to apply HR technology to manufacture a given product.
As may be seen, the analysis includes not only measurable economic aspects, but also in many cases non-measurable considerations of a technical, organisational and quality nature. Performance of an analysis that takes into account the specific nature of the product in question builds on the general lists of advantages and drawbacks to HR use that was discussed in Section 2.1. In specific sections the study may be made in a general way, as an estimation, or even with detailed calculations (see Section 2.3).
Content of a benefit analysis
Savings on materials and labour. A determination is made of the reduction in production costs resulting from the elimination or diminution of waste in the form of sprues and runners.
Figure 2.1 Feasibility study for the introduction of an HR system ECONOMIC CONDITIONS INITIAL ASSUMPTIONS FOR HR SYSTEM TECHNICAL CONDITIONS Benefit Analysis reduction in materials consumption shortening of production cycle reduction in servicing new production potential increased production better utilisation of injection machines Cost Analysis cost of HR mould cost of HR control equipment cost of modernising moulding workplace manufacturing costs Market Research
orders and their continuity expected profits raw material prices innovation aspects of production competitiveness market trends financing method form of payment ensuring solvency VAT exemptions Financial Potential Detailed scope of requirements HR system description Bidding procedure, discussion of system Selection of HR system and supplier
production type (product range) production volume (annual, overall) type of plastic
colour change frequency
Production Data purpose of product tolerances appearance certification Quality Requirements Factory Potential
type and nature of injection moulding machine
peripheral equipment degree of automation CAD/CAM
compatibility with factory development programme
personnel skills (design, performance, servicing, maintenance)
work system and organisation efficiency of decision-making system efficiency of supervisory system
supplier’s technical knowledge assistance in commissioning (simulations, design) availability of spare parts delivery (date, method) availability of price list experience of cooperation to date suggested areas of cooperation informal relations
This means:
• Reduction in raw materials consumption;
• Reduction of finishing work on mouldings (sprue removal);
• Curtailment of the waste recycling process (sorting, milling, drying, storage), leading in turn to a reduction in the number of regrinding machines, and savings on labour, energy consumption and production area required.
Example. In a typical 16-cavity mould (Figure 2.2) the quantity of waste for three types of gating will be compared. In layout (a), with cold runners throughout, the volume of sprue is some 25 cm3; in a type (b) mould with a simple HR system with four nozzles and
Figure 2.2 Comparison of waste arisings in mould
a - cold runner - 25 cm3 (approximately 17 t/y); b - HR system ending in cold runner - 5 cm3 (approximately 3.5 t/y); c - HR system - 0 cm3
a short CR, the volume of sprue has diminished to 5 cm3; while in a type (c) mould with a full HR system with sixteen nozzles, sprues and runners have been completely eliminated. Assuming a cycle time of 30 s, a type (a) mould will produce around 3 kg of waste per hour. In the course of a year, working a single shift, this will mean 48 weeks x 120 h x 3 kg = 17,280 kg. Thus one injection moulding machine will produce 17 tonnes of waste, which needs sorting, regrinding, possibly storing and then returning into production. A type (b) mould will give only 20% of this waste with a HR system of moderate cost, and this makes it competitive for medium production runs. A type (c) mould is expensive, but will pay for itself with production runs of suitable volume.
Increasing production through shortening of the cooling time and machine times and automation of work:
• A shortening of the cycle time is possible in two cases: when the cold sprue is considerably thicker than the moulding and governs the cooling time; and when the availability of greater pressure and injection speed enable wall thickness (e.g., of packaging items) to be reduced. Generally speaking, a fall in the cost of production of thin-walled mouldings may be expected. Where the mouldings are small and the share of sprue large, we may expect a further shortening of the cycle through a reduction in injection time and plasticisation time of what may sometimes be a several times smaller mass of plastic;
• Automatic and waste-free operation of HR moulds enables production to be continuous, even during holidays. In this respect the set comprising injection moulding machine, mould with HR and peripheral equipment may become a Flexible Work Centre (FWC). Simplified production. After sprues and runners are eliminated, automatic separators or manual sorting to separate them from the mouldings are no longer required, which makes the automation of work easier.
Improved utilisation of injection moulding machines. Use of moulds with HR makes it possible to:
• Increase the available shot volume through sprue elimination (it should be remembered, however, that the compressibility of the melt in HR demands an increase in the available shot volume by around 20% of the HR volume);
• Reduce the required injection and holding pressure; • Reduce the required locking force;
• Reduce energy consumption.
This not uncommonly leads to the selection of a smaller injection moulding machine and a reduction in machine costs.
New production potential. HR technology particularly enables the injection method to be employed to produce large-sized pieces. Examples of products where HR technology underpins the manufacture are, transport boxes, automobile bumpers and street waste bins. The restriction on their manufacture has been the length of the flow path and the associated problem of filling the mould cavity.
Analysis of outlay
This analysis includes investment costs and production costs directly and indirectly linked to the introduction of moulds with HR or HR and CR. The following costs must be accounted for:
• Purchasing moulds with HR;
• Control equipment - temperature regulators;
• Upgrading of the machinery stock, which most frequently means purchase of injection moulding machines;
• Equipment to automate work or raise the efficiency of automatic operations, for example, robots for rapid removal and management of travel of falling mouldings, to apply labels and so on;
• Equipment to monitor the ejection of mouldings;
• Process equipment underpinning the operation of the HR system; circulation thermostats and magnetic grids (see Section 3.4), special nozzles;
• Manufacture;
• Maintenance of operations (replacement of damaged heaters, seals, and so forth); • Staff training.
The outlay expended should, however, be related to the production volume (see Section 2.2) and the results of market research.
Market research
Professional market research, even in cases where orders are already in place, will allow rapid adaptation to current prices, the implementation of a flexible financial policy and a reduction in the degree of risk of undertaking manufacture. Specialists in this area look at the degree of innovation in the manufacture, competitiveness and trends in market development. Work in this field is covered by confidentiality clauses, just as company’s achievements in design, processes employed, equipment, and so on, should be.
Production data
The next factors that must be considered in deciding not only whether to use HR, but also in the subsequent choice of the optimum system, are:
• Definition of the detailed range, for example use of thin-walled pots with precise orders of magnitude;
• Production quantity - monthly, annually, overall;
• Type of plastic and introduction of additives to determine its processing conditions; • Frequency of colour changes in relation to supply batches.
Quality requirements
HR technology enables control of plastic pressures and temperatures to be enhanced, these being parameters that have an impact in shaping the internal and external quality properties (see Section 3.2).
In view of the compulsory need to automate operations, cycle time repetition conditions are created. This leads to a rise in what is known as machine capacity, Cm, and in process capacity, Cp, and this process may be under statistical control [2]. This in turn is one of the conditions
of quality production as required by the set of national standards EN ISO 9000-1 [3].
Factory potential
The factory potentials specified in Figure 2.1 may be taken as arguments for or against the use of HR. Technical development, though, is bringing about a situation where HR
technology is increasingly competitive, particularly for the economics of manufacturing mass-production items, and also as regards the quality of technical products.
Analysis of world trends shows that the most important factor in providing the conditions for use of HR is increasing employee skills.
When decisions are being taken about the use of HR and also subsequently, when the best system is being selected, the experience of HR system manufacturers should be utilised. Considerable assistance may be obtained from them in mould design and simulation of filling.
The initial principles put forward enable the requirements to be made specific, and then the optimum HR system to be selected for the production process in question (see Section 7).
Only now should the procedure of seeking offers and discussions to verify the system be commenced. Final choice of a supplier also depends on some other factors (see Figure 2.1 - Other factors concerning HR).