This article discusses failure mechanisms in tool and die materials that are very important to nearly all manufacturing processes. It is primarily devoted to failures of tool steels used in cold working and hot working applications. The processes involved in the analysis of tool and die failures are also covered. In addition, the article focuses on a number of factors that are responsible for tool and die failures, including mechanical design, grade selection, steel quality, machining processes, heat treatment operation, and tool and die setup.

This article describes the characteristics of tools and dies and the causes of their failures. It discusses the failure mechanisms in tool and die materials that are important to nearly all manufacturing processes, but is primarily devoted to failures of tool steels used in cold-working and hot-working applications. It reviews problems introduced during mechanical design, materials selection, machining, heat treating, finish grinding, and tool and die operation. The brittle fracture of rehardened high-speed steels is also considered. Finally, failures due to seams or laps, unconsolidated interiors, and carbide segregation and poor carbide morphology are reviewed with illustrations.

Several failed dies were analyzed and the results were used to evaluate fatigue damage models that have been developed to predict die life and aid in design and process optimization. The dies used in the investigation were made of H13 steels and fractured during the hot extrusion of Al-6063 billet material. They were examined to identify critical fatigue failure locations, determine corresponding stresses and strains, and uncover correlations with process parameters, design features, and life cycle data. The fatigue damage models are based on Morrow’s stress and strain-life models for flat extrusion die and account for bearing length, fillet radius, temperature, and strain rate. They were shown to provide useful information for the analysis and prevention of die failures.

A cross-recessed die of D5 tool steel fractured in service. The die face was found to be subjected to shear and tensile stresses as a result of the forging pressures from the material being worked. The presence of numerous slag stringers was revealed by microscopic examination of an unetched longitudinal section taken through the die. The pattern was microscopically revealed after etching with 5 % nital to be due to severe chemical segregation or banding. Considerable variation in the hardness, corresponding to the banded and non-banded regions across the face of the specimen was observed. The fracture was found to have originated near the high-stress region of the die face examination of the fracture surface. Failure of the die was concluded to have originated in an area of abnormally high hardness which is prone to microcracking during heat treatment for this grade of tool steel

This article focuses on the general root causes of failure attributed to the casting process, casting material, and design with examples. The casting processes discussed include gravity die casting, pressure die casting, semisolid casting, squeeze casting, and centrifugal casting. Cast iron, gray cast iron, malleable irons, ductile iron, low-alloy steel castings, austenitic steels, corrosion-resistant castings, and cast aluminum alloys are the materials discussed. The article describes the general types of discontinuities or imperfections for traditional casting with sand molds. It presents the international classification of common casting defects in a tabular form.

Two 38 mm (1.5 in.) diam threaded stud bolts that were part of a steel mold die assembly from a plastics molding operation were examined to determine their serviceability. Chemical analysis showed the material to be a plain carbon steel that approximated 1045. Visual examination revealed evidence of severe hammer blows to the clevis and boss areas and a gap between the die and the underside of the boss. Magnetic particle inspection showed cracks at the thread roots that, when examined metallographically, were found to contain MnS stringers. The cracking of the threads was attributed to a poor stud bolt design, which allowed a high stress concentration to occur at the base of the threads upon application of a lateral load. It was recommended that bolts of a new design that incorporated a stress-relieving groove be used. Threading of the bolt to eliminate the gap between the lower face of the boss and the die and an improved method of inserting or removing the bolt to avoid hammering (use of a wrench on a square or hexagonal boss) were also recommended.

A die-cast zinc adapter used in a snowthrower failed catastrophically in a brittle overload manner. The component had a chemical composition similar to standard zinc alloy ZA-27 (UNS Z35840), although the iron content was much higher and the copper slightly lower. The mechanical properties and alloy designation were not specified. Investigation (visual inspection, 187x SEM images, unetched 30x images, hardness testing, and chemical analysis) of both the failed adapter and an exemplar casting from known-good lot supported the conclusion that the casting failed as a result of brittle overload fracture due to excessive iron-zinc phase and gross porosity. These conditions acted synergistically to reduce the strength of the material. The composition was nonstandard, and the inherent brittleness suggested that it was unlikely that this material was an intentional proprietary alloy. No recommendations were made.

A forging die in a 250-ton press producing brass valves began to show signs of fatigue after a few thousand hits. By the time it reached 30,000 hits, the die was badly damaged and was submitted for analysis along with one of the last forgings produced. The investigation included visual and macroscopic inspection, metallographic and chemical analysis, SEM imaging, optical profilometry, mechanical property testing, and EDX analysis. The die was made of chromium hot-work tool steel and the forgings were made of CuZn39Pb3 heated to an initial working temperature 700 deg C. The entire surface of the die was covered with fatigue cracks and many fillets had been plastically deformed. Several other types of damage were also observed, including areas of oxidation, corrosion pits, voids, abrasive wear, die adhesion, and thermal fatigue. Fatigue cracking was the primary cause of failure with significant contributions from the other damage mechanisms.

A full lift disk, made of die cast brass, which served as a lifting aid in a safety valve, had cracked in service at a number of locations in the vicinity of the threaded hole. During microscopic examination, agglomeration of oxide inclusions were noted in the region of the cracks. Because the die cast brass was alloyed with aluminum, these inclusions consisted predominantly of aluminum oxide. The tolerable limit in pores and oxide inclusions was greatly exceeded in the lift disk under examination. Above all, the numerous oxide skins disrupted the cohesion of the microstructure and were primarily responsible for the failure of the lift disk.

This article describes the six fundamental factors that decide a tool's performance. These are mechanical design, grade of tool steel, machining procedure, heat treatment, grinding, and handling. A deficiency in any one of the factors can lead to a tool and die failure. The article presents a seven-step procedure to be followed when looking for the reason for a failure. A review of the results of the seven-point investigation may lead directly to the source of failure or narrow the field of investigation to permit the use of special tests.

An investigation was conducted to determine the factors responsible for the occasional formation of cracks on the parting lines of medium plain carbon and low-alloy medium-carbon steel forgings. The cracks were present on as-forged parts and grew during heat treatment. Examination revealed that areas near the parting line exhibited a large grain structure not present in the forged stock. High-temperature scale was also found in the cracks. It was concluded that the cracks were caused by material being folded over the parting line. The folding occurred because of a mismatch in the forgings and from material flow during trimming and/or material flow during forging.

The primary purpose of this article is to describe general root causes of failure that are associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be common sources of failure-inducing defects in the bulk working of wrought products. The article addresses the types of flaws or defects that can be introduced during the steel forging process itself, including defects originating in the ingot-casting process. Defects found in nonferrous forgings—titanium, aluminum, and copper and copper alloys—also are covered.

This article describes the general root causes of failure associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be the common sources of failure-inducing defects in bulk working of wrought products. The article discusses the types of imperfections that can be traced to the original ingot product. These include chemical segregation; ingot pipe, porosity, and centerline shrinkage; high hydrogen content; nonmetallic inclusions; unmelted electrodes and shelf; and cracks, laminations, seams, pits, blisters, and scabs. The article provides a discussion on the imperfections found in steel forgings. The problems encountered in sheet metal forming are also discussed. The article concludes with information on the causes of failure in cold formed parts.

Cluster bomb tailcone assemblies each containing two aluminum die-cast components were rejected because of the poor surface condition of the die castings. Numerous heat checks were found on the surfaces of the tailcones and radiographic inspection revealed inclusions, gas holes, and shrinkage defects in the castings. Most of the components failed to meet required mechanical properties because of these casting defects.

An AISI D2 tool steel insert from a forming die used in the manufacture of automotive components failed prematurely during production. Results of various analyses and simulation tests indicated fatigue failure resulting from improper heat treatment. The fatigue fracture originated because of a highly stressed condition produced by a sharp corner combined with low toughness from ineffective tempering. It was recommended that 25 other inserts that belonged to the same die be double tempered.

Near-surface porosity in zinc die castings that were subsequently plated with copper, nickel, and bright chromium was causing blemishes in the plating. Identifying die casting turbulence and hot spots were keys to process modifications that subsequently allowed porosity to be greatly minimized.

A segment from a premium-quality H13 tool steel die for die casting of aluminum failed after only 700 shots. The segment was subjected to visual, macroscopic, hardness, and metallographic testing. The investigation revealed that failure occurred as a result of fatigue at an electrical-discharge-machined surface where the resulting rehardened layer had not been removed. This rehardened layer had cracked, providing a source for fatigue initiation.

Extensive cracking was found in a batch of die-cast ZAMAK 3 solenoid valve seats during commissioning of the system in which they were installed. Scanning electron microscopic and chemical analyses conducted on one of the failed valve seats showed that the composition of the alloy was different from that specified. The presence of excess aluminum and lead impurities that had segregated to the grain boundaries, coupled with an inadequate amount of magnesium, resulted in intergranular corrosion and subsequent intergranular failure. Corrosion was accelerated by storage in a humid environment in a coastal area. It was recommended that proper chemical analysis of the zinc-aluminum alloy be carried out as a quality control procedure.

Lakes in zinc die castings are areas encompassed by irregular lines or waves on flat or slightly contoured surfaces which are intended to look uniform. The laked areas have to be removed by polishing before the castings can be plated. This adds considerably to the overall cost of production. Castings examined were of an automobile name-plate holder with two flat sides of approximately 113 sq cm. All castings produced during a trial showed laking defects, the number and position varying from casting to casting. It was found that formation of metal waves and lakes depended primarily on the design of the gate and runner system and operating conditions. High flow efficiencies, with adequate feeding to all sections of the die, and short cavity fill times are desirable.

Several surface-mount chip resistor assemblies failed during monthly thermal shock testing and in the field. The resistor exhibited a failure mode characterized by a rise in resistance out of tolerance for the system. Representative samples from each step in the manufacturing process were selected for analysis, along with additional samples representing the various resistor failures. Visual examination revealed two different types of termination failures: total delamination and partial delamination. Electron probe microanalysis confirmed that the fracture occurred at the end of the termination. Transverse sections from each of the groups were examined metallographically. Consistent interfacial separation was noted. Fourier transform infrared and EDS analyses were also performed. It was concluded that low wraparound termination strength of the resistors had caused unacceptable increases in the resistance values, resulting in circuit nonperformance at inappropriate times. The low termination strength was attributed to deficient chip design for the intended materials and manufacturing process and exacerbated by the presence of polymeric contamination at the termination interface.