Runner Design Guide Lines

Runner and gate design.

The Important Features

Introduction; The following is a brief summary of the important factors to consider when designing runner and gating systems for Zinc and Aluminium pressure die casting dies. In the past runner systems were designed using empirical knowledge and developed using trial and error methods which involved excessive time and often multiple die trials. Today, computer programmes exist which eliminate these problems and are able to give good results immediately but, many of the most basic design issues are often neglected during the design stage particularly if the die is designed by the tool maker without consultation to the die casting technicians. These brief notes are intended as guidelines for use during training and as an aide memoir for die design technicians and designers. They are not intended to cover all aspects of die design practice.

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Objective: The runner and gate system should achieve the following in basic terms:

Produce a casting of the specified quality; in terms of finish, size and tolerance, casting integrity, mechanical properties, cycle time and consistency.

Achieve first time success; to avoid wasted time on successive machine trials, delays in delivery of samples, loss of customer confidence and excessive die development costs.

Provide optimum yield; increases efficiency by optimising the casting to runner yield ratio, improve metal losses due to lower re-melt weights, reduces cycle times due to improved thermal efficiency.

THE BROCK METAL COMPANY LIMITED,WALSALL ROAD. NORTON CANES, CANNOCK, STAFFS, UK WS11 9NR.


Influencing factors.

Designing a runner system: Selection of the machine should be based on several factors but not just shot weight and platen area. Most machines are supplied with a PQ2 diagram or one exists from measurements taken on other similar machines. Runner designs should be based on machine performance with a given plunger or shot sleeve diameter, known hydraulic pressure and in the case of hot chamber die casting the nozzle size. Both projected area and lock tonnage should also be considered if the proposed runner plus casting is liable to approach the machine limits. Casting geometry: The cavity should be positioned to promote the best cavity fill conditions while accommodating essential die features such as core slides, cooling channels, sensitive casting features, number of cavities and robotic removal constraints. Other process criteria such as second operation locations, clipping orientation, break off de-gating and finishing requirements should also be considered before the cavity position is decided. Uniform flow path: The runner should establish a uniform metal flow rate deigned to promote the best hydraulic system, stable metal pressure and velocity. Most computer design programmes will control these features but the designer will still have institute a flow path allows these features conform to the desired parameters. Cavity fill conditions: Modern pressure die casting machines often have more power at the shot end than is required to achieve the optimum fill conditions. Consequently, the performance offers many gate area options capable of achieving the desired fill conditions the designer must select the most suitable based on the casting specification and process limitations. Cavity fill pattern: Is invariably decided by the casting geometry and gate position but the metal pressure and velocity will have influence but to a lesser extent. The influence of casting features such as vertical surfaces and ribs, variable section thicknesses, isolated bosses and cores must be considered when the gate position is decided. Venting and overflow wells: Should all be considered at the design stage are directly related to the cavity fill conditions and casting geometry but also the introduction of over flow wells or pockets may have significant cost implications.



Machine Performance.

Effects of change. Injection pressure: Reduce or increase.

Increased injection pressure will increase flash, raise galvanising and die erosion. Optimum pressure levels will improve casting integrity, maintain speed and velocity and improve cavity fill conditions. Reduced injection pressure reduces flow rates, and static metal pressure on hot chamber pressure die casting machines.

Plunger diameter on hot chamber die casting machines smaller plungers give the best casting results with higher injection pressure and faster delivery. On aluminium cold chamber machines plunger diameter choice is less critical but effect is far more significant in performance terms - increasing delivery velocity and reducing cavity fill times.

Plunger speeds - high terminal velocities can produce pressure spikes on older die casting machines leading flash and die wear. High gate speeds result in expensive die maintenance due to die erosion and galvanising.

Runner Area/volume - die designer should create a uniform flow through the runner by establishing nozzle area (hot chamber) as the largest section in the runner. Progressively reducing the cross sectional area of the runner at each section to the gate which should be the smallest area in the runner system. Similarly, on cold chamber dies the sprue post runner should be the largest runner section down to the gate which should be smallest section of the runner.

Flow rate histogram.

No

zzle

are

a

Gate Area



Runner features

Y Junction not T

Y Junction

Reduces area and increases pressure progressively.

T Junction Increases volume at the junction creating low pressure area at the centre of the gate.

ATHE BROCK METAL COMPANY LIMITED,WALSALL RO D. NORTON CANES, CANNOCK, STAFFS, UK WS11 9NR.


Runner features

Taper tangential runner - with shock absorber showing section change A to B to

Smaller diagram illustrates poor runner design small access radius,

increased e taper,

maintain pressure and velocity

runner volume at the radius, small runner cross section at the end of th

and no shock absorber.

THE BROCK METAL COMPANY LIMITED,WALSALL RO D. NORTO NES, CANNOCK, STAFFS, UK WS11 9NR. A N CA


Runner features

Drawings Show section through sprue posts on Aluminium (top) and Zinc (bottom)

This area most commonly inte d incorrectly by toolmakers. Note; Th radius

dies. rprete

e reduction from the sprue faces to die face and the size and blendwhich are struck from the same centre to ensure even transition from sprue to die.

THE BROCK METAL COMPANY LIMITED, WALSALL ROAD,. NORTON CANES, CANNOCK, STAFFS, UK WS11 9NR.


Runner features

Runner sections: Need to be adjusted by differing percentages to

r l 10% reduction in runner

area- down stream of metal

accommodate larger angular direction changes

30% reduction in runner a ea - down stream of meta

flow for 900 bend. flow for a 200 bend.

THE BROCK METAL COMPANY LIMITED, WALSALL ROAD. NORTON CANES, CANNOCK, STAFFS, UK WS11 9NR,


Gate Areas

ate Areas: ptimum for Zinc alloy pressure die-casting:

ed / velocity 35 45 metres per second. ish 20 milli seconds or functional

Optimum for Aluminium alloy pressure die casting: 5 metres per second.

. ortant on large castings as

Fil a

etry: has the largest influence on cavity flow paths high metal velocity pplied to vertical casting faces causes turbulence, galvanising and impedes metal. All of which

and areas; It is possible to assess parts of the casting separately nd this may be advantageous if they are unlikely to be fed directly from the gate.

of a given part sing separate gates for each zoned area. This will often improve fill characteristics

low: It must be stressed that the gates and runner both fluence flow direction. Once the runner is established metal under pressure will

GO

Gate spe Cavity fill time plated or powder coated fin

parts 40 milli seconds. Gate depth 0.15 0.5 mm. Gate speed / velocity 25 to 3

To avoid die erosion and control cavity fill characteristics Cavity fill time end of fill temperature is most imp

solidification can occur prior to cavity filling. Depth 1.25 3 mm (1.5 mm minimum for machine intensification to be effective). l P ttern:

Casting geomacan result in expensive die repairs / maintenance. Section changes and cores change pressure and direction and these effects need to be considered and understood when considering gate position options. Zones volumesaUsing computer programmes allows each separate zone to be quantified in volume and surface area terms. If treated as un-gated the fill time and end of fill temperature can be determined as a comparison with the main body of the total casting. Gating separate zones: It is possible also to examine separate zones uand reduce the risks of defects. The uses of multiple gates are not a risk if designed and implemented correctly. Runner will direct metal finenter the cavity in the same direction and flow angle. Varying injection speed and metal pressure may alter this angle slightly but this is only a fine tuning method.

THE BROCK METAL COMPANY LIMITED, WALSALL ROAD. NORTO NES, CANNOCK, STAFFS, UK WS11 9NR,N CA


Fill pattern.

Influence of casting geometryertain casting shapes are best filled in a predetermined way, if the tooling

re the depth is 50% of the edge length or more he box

: Cconfiguration allows. Deep boxes, whecan be fed using the gate runner configuration shown below alternatively tcan be turned through 450 to shorten the runner distance and improve shot yield.



Fill pattern.

vals or round castings: Try to fill the centre first using either a runner onfiguration below or a more traditional fan feed. With fan feeds it is essential to get

Octhe ratio of the approach angle and width of gate correct.



Fill pattern.

nnular rings: Can be fed using the runner configuration indicated below. A small ver flow well should positioned in the centre hole to take away any lubrication fume

Aoand another well placed on the out side perimeter adjacent to the last segment of the part to fill.



Fill pattern.

Rectangular Plates: Fill across shortest distance whenever possible t cut down ow distance and increase end of fill temperature. It is therefore advisable to avoid

oflthe option shown in the upper diagram if possible.



Fill pattern.

Diagram show e to resolve problems of porosity and poor ximately 6 mm deep, with a gate depth of between 1.8 and 2.5 mm. Casting weighed approximately 5 Kg and with a flow distance of 510 m

s: runner developed over a period of tim fill results. The darker blue area is appro

m.



Fill pattern.

Diagram show niform gate thickness of 2 mm. The runner and a subsequent increase in yield of 18% and a reduction in pr ected area of some 22% allowing improved shot speed and increased in injec

s: Revised runner with balance fill and ushows reduced shot weight by over 1 Kg

ojtion pressure.



Vents and Overflow wells.

Points to remember:

Over flow w tal flow, but rarely removegas and fume as the cavity is normal sealed before they become a .

only work for less than half of the cavity fill time as they are final fill is achieved.

Over flow wells are a poor method of die heating both inefficient and wasteful.

See reference material from ILZRO, IZA.

JWT Sep

ells can be used to change or divert me ctively

Similarly vents can sealed off before the

Use only one connection per over flow to avoid back feeding through the

overflow and reintroducing gas and cold metal.

Always vent over flow wells as a precaution.

Many are lost before re-melting and therefore increase metal losses.

t 05 issue 5

JWT

Runner Design Guide Lines

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